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Parity Conditions in International Finance and
Currency Forecasting

It is not for its own sake that men desire money, but for the sake of what they can
purchase with it.

Adam Smith (1776)

Learning Objectives

To describe the meaning of the
“law of one price” and its importance to the study of
international finance

To explain how arbitrage links goods prices and asset returns internationally

To list and describe the five key theoretical relationships among spot exchange rates,
forward exc
hange rates, inflation rates, and interest rates that result from international
arbitrage activities

To differentiate between the real and nominal exchange rate and the real and nominal
interest rate

To list and describe the four requirements for succe
ssful currency forecasting

To identify a five
stage procedure for forecasting exchange rates in a fixed
rate system

To describe how to forecast exchange rates in a floating
rate system using the predictions
already embodied in interest and forward rate

To describe the meaning and likelihood of forecasting success in both fixed
rate and
rate systems

Key Terms


market exchange


capital market integration

capital market


carry trade


covered interest

covered interest


currency forecasting

Fisher effect (FE)

forward discount

forward premium

fundamental analysis

inflation differential

interest rate differential

interest rate parity (IRP)

international Fisher effect (IFE)

law of one

based forecasts

based forecasts

nominal exchange rate

nominal interest rate

parity conditions

peso problem

purchasing power parity (PPP)

real exchange rate

real interest rate

technical analysis

trend analysis

unbiased forward rate (UFR)

unbiased predictor

n the basis of the flows of goods and capital discussed in
Chapter 2
, this chapter presents a
simple yet elegant set of equilibrium relationships that should apply to product prices, interest
rates, and spot and forward exchange rates i
f markets are not impeded. These relationships, or
parity conditions,

provide the foundation for much of the remainder of this text; they should
be clearly understood before you proceed further. The final section of this chapter examines the
usefulness of
a number of models and methodologies in profitably forecasting currency
changes under both fixed
rate and floating
rate systems.


Arbitrage and the Law of One Price


is one of the most important concepts in all of finance. It is ordinarily def
ined as
the simultaneous purchase and sale of the same assets or commodities on different markets to
profit from price discrepancies. The concept of arbitrage is of particular importance in
international finance because so many of the relationships between

domestic and
international financial markets, exchange rates, interest rates, and inflation rates depend on
arbitrage for their existence. Indeed, by linking markets together, arbitrage underlies the
globalization of markets.

One of the central ideas of i
nternational finance stems from arbitrage: In competitive
markets, characterized by numerous buyers and sellers having low
cost access to
information, exchange
adjusted prices of identical tradable goods and financial assets must
be within transaction cost
s of equality worldwide. This idea, referred to as the
law of one

is enforced by international arbitrageurs who follow the profit
guaranteeing dictum of
“buy low, sell high” and prevent all but trivial deviations from equality. Similarly, in the
ence of market imperfections, risk
adjusted expected returns on financial assets in
different markets should be equal.

Five key theoretical economic relationships, which are depicted in
Exhibit 4.1
, result from
these arbitrage activities:

Purchasing powe
r parity (PPP)

Fisher effect (FE)

International Fisher effect (IFE)

Interest rate parity (IRP)

Forward rates as unbiased predictors of future spot rates (UFR)

The framework of
Exhibit 4.1

emphasizes the links among prices, spot exchange rates,
rest rates, and forward exchange rates. Before proceeding, some explanation of
terminology is in order. Specifically, a foreign currency is said to be at a
forward discount

the forward rate expressed in dollars is below the spot rate, whereas a

exists if the forward rate is above the spot rate. The forward discount or premium is
expressed in annualized percentage terms as follows:

Exhibit 4.1

Five Key Theoretical Relationships Among Spot
Rates, Forward Rates, inflation Rates, and Inter
est Rates

where the exchange rate is stated in domestic currency units per unit of foreign currency.

According to the diagram in
Exhibit 4.1
, if inflation in, say, Mexico is expected to exceed
inflation in the United States by 3% for the coming year,
then the Mexican peso should
decline in value by about 3% relative to the dollar. By the same token, the one
year forward
Mexican peso should sell at a 3% discount relative to the U.S. dollar. Similarly, one
interest rates in Mexico should be about 3%

higher than one
year interest rates on securities
of comparable risk in the United States.

The common denominator of these parity conditions is the adjustment of the various rates
and prices to inflation. According to modern monetary theory, inflation is
the logical
outcome of an expansion of the money supply in excess of real output growth. Although this
view of the origin of inflation is not universally subscribed to, it has a solid microeconomic
foundation. In particular, it is a basic precept of price
theory that as the supply of one
commodity increases relative to supplies of all other commodities, the price of the first
commodity must decline relative to the prices of other commodities. Thus, for example, a
bumper crop of corn should cause corn's valu
e in exchange

its exchange rate

to decline.
Similarly, as the supply of money increases relative to the supply of goods and services, the
purchasing power of money

the exchange rate between money and goods

must decline.

The mechanism that brings this adjus
tment about is simple and direct. Suppose, for example,
that the supply of U.S. dollars exceeds the amount that individuals desire to hold. In order to
reduce their excess holdings of money, individuals increase their spending on goods,
services, and secur
ities, causing U.S. prices to rise. Moreover, as we saw in
Chapter 2
, this
price inflation will cause the value of the dollar to decline.

The adverse consequences of an expansionary monetary policy and the benefits of a
monetary policy

one that
leads to stable prices and is not subject to sharp expansions or

are both illustrated in “Bolivia Ends Its Hyperinflation.”


Bolivia Ends Its Hyperinflation

In the spring of 1985, Bolivia's inflation rate was running at 101,000%
a year, one of the
highest rates in history. At the time, Bolivian government revenues covered less than 15% of
its spending, with most of the rest being paid for by printing new pesos. Inflation threatened
the very fabric of society. Prices changed by the

minute, and people literally carried money
around in suitcases. Currency, which was printed abroad, was the third
largest import in
1984. The two
inch stack of money needed to buy a chocolate bar far outweighed the candy.
The government eventually solved
the stacks
money problem by issuing notes in
denominations of 1 million, 2 million, and 10 million pesos. But its failure to solve the
inflation problem led to its replacement by a new government that announced an anti
inflation program on August 29, 19
85. The program had two basic thrusts: Cut spending and
shut down the printing presses. To cut spending, the new government adopted the simple rule
that it would not spend more than it received. Each day the finance minister signed checks
only up to the va
lue of the revenues the Treasury had received that day

regardless of the
spending that had been budgeted. By October, the monthly inflation rate had fallen below
zero, from more than 60% in August (see
Exhibit 4.2
). Economists consider this performance
be a singular verification of basic monetary theory.

Exhibit 4.2

Bolivia Ends Its Hyperinflation in 1985 by Shutting
Down the Printing Presses

: IMF Statistics.

A further link in the chain relating money
supply growth, inflation, interest rates, a
exchange rates is the notion that money is neutral. That is, money should have no impact on
real variables. Thus, for example, a 10% increase in the supply of money relative to the
demand for money should cause prices to rise by 10%. This view has impor
tant implications
for international finance. Specifically, although a change in the quantity of money will affect
prices and exchange rates, this change should not affect the rate at which domestic goods are
exchanged for foreign goods or the rate at which

goods today are exchanged for goods in the
future. These ideas are formalized as purchasing power parity and the Fisher effect,
respectively. We will examine them here briefly and then in greater detail in the next two

The international analogue

to inflation is home currency depreciation relative to foreign
currencies. The analogy derives from the observation that inflation involves a change in the
exchange rate between the home currency and domestic goods, whereas home currency

a de
cline in the foreign currency value of the home currency

results in a
change in the exchange rate between the home currency and foreign goods.

That inflation and currency depreciation are related is no accident. Excess money
growth, through its impa
ct on the rate of aggregate spending, affects the demand for goods
produced abroad as well as goods produced domestically. In turn, the domestic demand for
foreign currencies changes, and, consequently, the foreign exchange value of the domestic
currency c
hanges. Thus, the rate of domestic inflation and changes in the exchange rate are
jointly determined by the rate of domestic money growth relative to the growth of the amount
that people

domestic and foreign

want to hold.

If international arbitrage enforce
s the law of one price, then the exchange rate between the
home currency and domestic goods must equal the exchange rate between the home currency
and foreign goods. In other words, a unit of home currency (HC) should have the same
purchasing power worldwi
de. Thus, if a dollar buys a pound of bread in the United States, it
should also buy a pound of bread in Great Britain. For this to happen, the foreign exchange
rate must change by (approximately) the difference between the domestic and foreign rates of
flation. This relationship is called
purchasing power parity


Similarly, the
nominal interest rate,

the price quoted on lending and borrowing transactions,
determines the exchange rate between current and future dollars (or any other currency). For
xample, an interest rate of 10% on a one
year loan means that one dollar today is being
exchanged for 1.1 dollars a year from now. But what really matters, according to the Fisher
effect (FE), is the exchange rate between current and future purchasing powe
r, as measured
by the real interest rate. Simply put, the lender is concerned with how many more goods can
be obtained in the future by forgoing consumption today, whereas the borrower wants to
know how much future consumption must be sacrificed to obtain
more goods today. This
condition is the case regardless of whether the borrower and lender are located in the same or
different countries. As a result, if the exchange rate between current and future goods

real interest rate

varies from one country to
the next, arbitrage between domestic and
foreign capital markets, in the form of international capital flows, should occur. These flows
will tend to equalize real interest rates across countries. By looking more closely at these and
related parity conditio
ns, we can see how they can be formalized and used for management

Case Oil Levies and the Law of One Price

The combination of weakening oil prices in the mid
1980s and the failure of Congress to
deal with the budget deficit by cutting spendi
ng led some to see the possibility of achieving
two objectives at once: (1) protecting U.S. oil producers from “cheap” foreign competition
and (2) reducing the budget deficit. The solution was an oil
import fee or tariff. A tax on
imported crude oil and re
fined products that matches a world oil price decline, for example,
would leave oil and refined
product prices in the United States unchanged. Thus, it was
argued, such a tax would have little effect on U.S. economic activity. It would merely
represent a t
ransfer of funds from foreign oil producers to the U.S. Treasury. Moreover, it
would provide some price relief to struggling refineries and encourage the production of
U.S. oil. Finally, at the current level of imports, a $5/barrel tariff on foreign crude
oil and a
separate tariff of $10/barrel
equivalent on refined products would raise more than $11.5
billion a year in revenue for the U.S. Treasury.



Suppose the tariff were levied solely on imported crude. In an integrated world
economy, who
would be hurt? Who would benefit? Why? What would be the longer


If a $10/barrel tariff were levied on imported refined products (but no tariff were
levied on crude oil), who would benefit? Who would be hurt? Why? What would be the
term consequences?


What would be the economic consequences of the combined $5/barrel tariff on
imported crude and a $10/barrel tariff on refined oil products? How will these tariffs
affect domestic consumers, oil producers, refiners, companies compe
ting against imports,
and exporters?


How would these proposed import levies affect foreign suppliers to the United
States of crude oil and refined products?


During the 1970s price controls on crude oil

but not on refined products

in effect in
the United States. Based on your previous analysis, what differences would
you expect to see between heating oil and gasoline prices in New York and in Rotterdam
(the major refining center in northwestern Europe)?


Purchasing Power Parity

Purchasing po
wer parity (PPP)

was first stated in a rigorous manner by the Swedish
economist Gustav Cassel in 1918. He used it as the basis for recommending a new set of
official exchange rates at the end of World War I that would allow for the resumption of
normal tra
de relations.

Since then, PPP has been widely used by central banks as a guide to
establishing new par values for their currencies when the old ones were clearly in
disequilibrium. From a management standpoint, purchasing power parity is often used to
ecast future exchange rates, for purposes ranging from deciding on the currency
denomination of long
term debt issues to determining in which countries to build plants.

In its

version, purchasing power parity states that price levels should be equ
worldwide when expressed in a common currency. In other words, a unit of home currency
should have the same purchasing power around the world. This theory is just an application
of the law of one price to national price levels rather than to individual
prices. (That is, it
rests on the assumption that free trade will equalize the price of any good in all countries;
otherwise, arbitrage opportunities would exist.) However, absolute PPP ignores the effects on
free trade of transportation costs, tariffs, qu
otas and other restrictions, and product

The Big Mac index, a light
hearted guide to whether currencies are at their “correct” levels
against the dollar, illustrates the law of one price and absolute purchasing power parity. It is
ed by comparing the prices of Big Macs worldwide (they are produced in almost 120
countries). The Big Mac PPP, put together by
The Economist,

is the exchange rate that would
leave hamburgers costing the same overseas as in the United States. By comparing B
ig Mac
PPPs with actual exchange rates, which is done in
Exhibit 4.3
, we can see whether a currency
is over

or undervalued by this standard.

For example, a Big Mac in Britain cost £1.99 on July 7, 2007. Dividing this price by its U.S.
price of $3.41 impli
es a PPP exchange rate of £0.58/$:

The actual exchange rate on that date was £0.50. By this measure, the pound was 16%
overvalued on July 7, 2007:

Alternatively, with a dollar PPP of HK$3.53/$ (HK$12/$3.41), the Hong Kong dollar
appeared to be underval
ued by 55% (HK$3.52/7.82 − 1 = − 55%).

The Big Mac standard is somewhat misleading because you are buying not just the
hamburger but also the location. Included in the price of a Big Mac is the cost of real estate,
local taxes, and local services, which di
ffer worldwide and are not traded goods. When the
items being compared contain a bundle of traded and nontraded goods and services, as in the
case of a Big Mac, it should not be surprising that absolute PPP and the law of one price fail
to hold. Despite it
s flaws, the Big Mac index has had some success. For example, in 1999, it
signaled that the euro was overvalued at its launch and the euro fell, notwithstanding
expectations to the contrary. In 2002, it signaled that the U.S. dollar was more overvalued
n at any other time in the life of the Big Mac index; shortly there
after, the dollar
plummeted in value. Similarly, the Big Mac index's signal in 2007 that the euro and the
pound were overvalued relative to the U.S. dollar (as shown in
Exhibit 4.3
) preced
ed steep
declines in the dollar values of these currencies in mid


version of purchasing power parity, which is used more commonly now, states
that the exchange rate between the home currency and any foreign currency will adjust to
t changes in the price levels of the two countries. For example, if inflation is 5% in the
United States and 1% in Japan, then the dollar value of the Japanese yen must rise by about
4% to equalize the dollar price of goods in the two countries.

Exhibit 4.

The Big Mac Hamburger Standard as of July 7,

*Purchasing power parity: local currency price divided by dollar price in the United

**Under/over valuation: (implied PPP rate

actual exchange rate)/actual exchange rate.


Average of New Yor
k, Chicago, San Francisco, and Atlanta prices.


Average of prices in the euro area.


The Economist.

Formally, if

and i

are the periodic price
level increases (rates of inflation) for the home
country and the foreign country, respectively;

is the dollar (HC) value of one unit of
foreign currency at the beginning of the period; and

is the spot exchange rate in period


Equation 4.2

holds, then

The value of

appearing in
Equation 4.3

is known as the
PPP rate.

For example, if the
United States and Switzerland are running annual inflation rates of 5% and 3%, respectively,
and the spot rate is SFr 1


then according to
Equation 4.3

the PPP rate for the Swiss
franc in three years should be

If purchasing power parity is expected to hold, then $0.7945/SFr is the best prediction for the
Swiss franc spot rate in three years. The one
period version of
Equation 4.3

is commonly
used. It is


Calculating the PPP Rate for the
Swiss Franc

Suppose the current U.S. price level is at 112 and the Swiss price level is at 107, relative to
base price levels of 100. If the initial value of the Swiss f
ranc was $0.98, then according to
PPP, the dollar value of the franc should have risen to approximately $1.0258 [0.98 X
(112/107)], an appreciation of 4.67%. On the other hand, if the Swiss price level now
equals 119, then the franc should have depreciated

by about 5.88%, to $0.9224 [0.98 X

Purchasing power parity is often represented by the following approximation of

That is, the exchange rate change during a period should equal the
inflation differential

that same time per
iod. In effect, PPP says that
currencies with high rates of inflation should
depreciate relative to currencies with lower rates of inflation.

Exhibit 4.4

Purchasing Power Parity

Equation 4.5

is illustrated in
Exhibit 4.4
. The vertical axis measures the
percentage currency
change, and the horizontal axis shows the inflation differential. Equilibrium is reached on the
parity line, which contains all those points at which these two differentials are equal. At point
A, for example, the 3% inflation different
ial is just offset by the 3% appreciation of the
foreign currency relative to the home currency. Point B, on the other hand, depicts a situation
of disequilibrium, at which the inflation differential of 3% is greater than the appreciation of
1% in the HC v
alue of the foreign currency.

The Lesson of Purchasing Power Parity

Purchasing power parity bears an important message: Just as the price of goods in one year
cannot be meaningfully compared with the price of goods in another year without adjusting
for interim inflation, so exchange rate changes may indicate nothing more t
han the reality
that countries have different inflation rates. In fact, according to PPP, exchange rate
movements should just cancel out changes in the foreign price level relative to the domestic
price level. These offsetting movements should have no effe
cts on the relative competitive
positions of domestic firms and their foreign competitors. Thus, changes in the
exchange rate

that is, the actual exchange rate

may be of little significance in
determining the true effects of currency changes on a
firm and a nation. In terms of
currency changes affecting relative competitiveness, therefore, the focus must be not on
nominal exchange rate changes but instead on changes in the real purchasing power of one
currency relative to another. Here we consider
the concept of the real exchange rate.

real exchange rate

is the nominal exchange rate adjusted for changes in the relative
purchasing power of each currency since some base period. In technical terms, the real
exchange rate at time

(dollars or HC pe
r unit of foreign currency),

, relative to the base
period (specified as time 0) is defined as


is the foreign price level and

the home price level at time t, both indexed to 100
at time 0.

By indexing these price levels to 100 as of the ba
se period, their ratio reflects the change in
the relative purchasing power of these currencies since time 0. Note that increases in the
foreign price level and foreign currency depreciation have offsetting effects on the real
exchange rate. Similarly, hom
e price
level increases and foreign currency appreciation
offset each other.

An alternative

and equivalent

way to represent the real exchange rate is to directly
reflect the change in relative purchasing powers of these currencies by adjusting the
exchange rate for inflation in both countries since time 0, as follows:

where the various parameters are the same as those defined previously.

If changes in the nominal exchange rate are fully offset by changes in the relative price
levels between the tw
o countries, then the real exchange rate remains unchanged. (Note
that the real exchange rate in the base period is just the nominal rate

Specifically, if
PPP holds, then we can substitute the value of

Equation 4.2

Equation 4.6
Making th
is substitution yields

; that is, the real exchange rate remains constant at

Alternatively, a change in the real exchange rate is equivalent to a deviation from PPP.


Calculating the Real Exchange
Rate for the Japanese Yen

1982 and 2006, the ¥/$ exchange rate moved from ¥249.05/$ to ¥116.34.
During this same 25
year period, the consumer price index (CPI) in Japan rose from
80.75 to 97.72 and the U.S. CPI rose from 56.06 to 117.07.


If PPP had held over this period, what wo
uld the ¥/$ exchange rate have been in


According to
Equation 4.2
, in 1995, the ¥/$ exchange rate should have been

In working this problem, note that
Equation 4.3

was inverted because we are expressing
the exchange rate in ¥/$ t
erms rather than $/¥ terms. Note too that the ratio of CPIs is
equal to the cumulative price
level increase. Comparing the PPP rate of ¥144.32/$ to
the actual rate of ¥116.34/$, we can see that the yen has appreciated more than PPP
would suggest.


What h
appened to the real value of the yen in terms of dollars during this period?


To estimate the real value of the yen, we convert the exchange rate from ¥/$
terms to $/¥ terms and apply
Equation 4.5

(using the yen quoted in ¥/$ terms would
yield us
the real value of the U.S. dollar in terms of yen):

To interpret this real exchange rate and see how it changed since 1982, we compare it
to the real exchange rate in 1982, which just equals the nominal rate at that time of
1/249.05 = $0.004015/¥(becaus
e the real and nominal rates are equal in the base
period). This comparison reveals that during the 25
year period from 1982 to 2006, the
yen appreciated in real terms by (0.004981 − 0.004015)/0.004015 = 24%. This dramatic
appreciation in the inflation
usted value of the Japanese yen put enormous
competitive pressure on Japanese exporters as the dollar prices of their goods rose far
more than the U.S. rate of inflation would justify.

The distinction between the nominal exchange rate and the real exchange

rate has
important implications for foreign exchange risk measurement and management. As we
will see in
Chapter 11
, if the real exchange rate remains constant (i.e., if purchasing power
parity holds), currency gains or losses from nominal exchange rate ch
anges will generally
be offset over time by the effects of differences in relative rates of inflation, thereby
reducing the net impact of nominal devaluations and revaluations. Deviations from
purchasing power parity, however, will lead to real exchange ga
ins and losses. In the case
of Japanese exporters, the real appreciation of the yen forced them to cut costs and develop
new products less subject to pricing pressures. We will discuss their responses in more
detail in
Chapter 11


Gustav Cassel, “Abnormal Deviations in International Exchanges,”
, December 1918, pp. 413


Dividing both sides of
Equation 4.4


and then subtracting 1 from both sides

Equation 4.5

follows if

is relatively small.

Expected Inflation and Exchange Rate Changes

Changes in expected, as well as actual, inflation will cause exchange rate changes. An
increase in a currency's expected rate of inflation, all other things being equal, makes that
currency more expensive to hol
d over time (because its value is being eroded at a faster
rate) and less in demand at the same price. Consequently, the value of higherinflation
currencies will tend to be depressed relative to the value of lower
inflation currencies, other
things being e

The Monetary Approach

More recently, purchasing power parity has been reformulated into the
monetary approach

to exchange rate determination. It is based on the
quantity theory of money:


is the national money supply,

is the general price

is real GNP, and

the velocity of money.

We can rewrite
Equation 4.8

in terms of growth rates to give the determinants of domestic




the domestic inflation rate



the rate of domestic money supply expansion



the growth in real domestic GNP



the change in the velocity of the domestic money supply

For example, if U.S. money
supply growth is forecast at 5%, real GNP is expected to grow
at 2%, and the velocity of money is expected to fall by 0.5%, then
ion 4.9

that the U.S. inflation rate will be 5%





A similar equation will hold for the predicted foreign rate of inflation. Combining these
two equations along with purchasing power parity leads to the following predicted
ange rate change:

where the subscript

refers to the corresponding rates for the foreign country.


Dividing both current price levels by their base levels effectively indexes each to
100 as of the base period.

Empirical Evidence

The strictest version of purchasing power parity

that all goods and financial assets obey
the law of one price

is demonstrably false. The risks and costs of shipping goods
internationally, as well as government
erected barriers to trade and capital flows,
are at
times high enough to cause exchange
adjusted prices to systematically differ between
countries. As shown in
Exhibit 4.5
, retail prices of Oakley's Monster Dog sunglasses
clearly vary around the world, from $97.53 in New York City to $169.02 in Rome.

On the
other hand, there is clearly a relationship between relative inflation rates and changes in
exchange rates. In particular, over time, as shown in
Exhibit 4.6
, those currencies with the
largest relative decline (gain) in purchasing power saw the sha
rpest erosion (appreciation)
in their foreign exchange values.

The general conclusion from empirical studies of PPP is that the theory holds up well in the
long run, but not as well over shorter time periods.

The difference between the short
and long
run effects can be seen in
Exhibit 4.7
, which compares the actual dollar exchange
rate for six countries with their PPP rates. Despite substantial short
run deviations from
purchasing power parity, currencies have a distinct tendency to move toward their P
predicted rates. Another way to view this evidence is that, despite fluctuations, the real
exchange rate tends to revert back to its predicted value of e
. That is, if

, then the real
exchange rate should fall over time toward e
, whereas if

, the real exchange rate
should rise over time toward

Additional support for the existence of mean
behavior of real exchange rates is provided by data spanning two centuries on the dollar
sterling and French franc
sterling real exchange rat

Mean reversion has important
implications for currency risk management, which will be explored in
Chapter 11

Exhibit 4.5

Retail Prices Around the World for Oakley's
Monster Dog Sunglasses


Retail prices for Oakley model 05
103 as presented in the
Wall Street Journal,

September 26, 2007, p. D4.

Exhibit 4.6

Purchasing Power Parity Empirical Data,



International Monetary Fund; Federal Reserve Bank of New York.

Exhibit 4.7

Purchasing Power Party and Actual Exchange


Actual exchange rates obtained from Federal Reserve Bank of New York.
Inflation data from International Monetary Fund, World Economic Outlook Database,
April 2007.

A common explanation for the fail
ure of PPP to hold is that goods prices are sticky, leading
to short
term violations of the law of one price. Adjustment to PPP eventually occurs, but it
does so with a lag. An alternative explanation for the failure of most tests to support PPP in
the sho
rt run is that these tests ignore the problems caused by the combination of
differently constructed price indices, relative price changes, and nontraded goods and
services. Despite these problems, most tests of relative PPP as a long
term theory of
e rate determination seem to support its validity.

In summary, despite often lengthy departures from PPP, there is a clear correspondence
between relative inflation rates and changes in the nominal exchange rate. However, for
reasons that have nothing nece
ssarily to do with market disequilibrium, the correspondence
is not perfect.


President Carter Lectures the
Foreign Exchange Markets

At a press conference in March 1978, President Jimmy Carter

responding to a falling

lectured the internat
ional financial markets as follows:

I've spent a lot of time studying about the American dollar, its value in international
monetary markets, the causes of its recent deterioration as it relates to other major
currencies. I can say with complete assurance
that the basic principles of monetary
values are not being adequately addressed on the current international monetary market.

President Carter then offered three reasons why the dollar should improve: (1) the
“rapidly increasing” attractiveness of investme
nt in the U.S. economy as a result of high
nominal interest rates, (2) an end to growth in oil imports, and (3) a decline in the real
growth of the U.S. economy relative to the rest of the world's economic growth.



How were financial markets li
kely to respond to President Carter's lecture?


At the time President Carter made his remarks, the inflation rate was running at
about 10% annually and accelerating as the Federal Reserve continued to pump up the
money supply to finance the grow
ing government budget deficit. Meanwhile, the
interest rate on long
term Treasury bonds had risen to about 8.5%. Was President
Carter correct in his assessment of the positive effects on the dollar of the higher
interest rates? Explain. Note that during 19
77, the movement of private capital had
switched to an outflow of $6.6 billion in the second half of the year, from an inflow of
$2.9 billion in the first half.


Comment on the consequences of a reduction in U.S. oil imports for the value of
the U.S. dol
lar. Next, consider that President Carter's energy policy involved heavily
taxing U.S. oil production, imposing price controls on domestically produced crude oil
and gasoline, and providing rebates to users of heating oil. How was this energy policy

to affect the value of the dollar?


What were the likely consequences of the slowdown in U.S. economic growth for
the value of the dollar? For the U.S. trade balance?


If President Carter had listened to the financial markets, instead of trying to
ture them, what might he have heard? That is, what were the markets trying to tell
him about his policies?


Perhaps the best known of these studies is Henry J. Gailliot, “Purchasing Power
Parity as an Explanation of Long
Term Changes in Exchange Rates,”
Journal of Money,
Credit, and Banking,

August 1971, pp. 348



See James R. Lothian and Mark P. Taylor, “Real Exchange Rate Behavior: The
Recent Float from the Perspective of the Past Two Centuries,”
Journal of Political

June 1996.


The F
isher Effect

The interest rates that are quoted in the financial press are nominal rates. That is, they are
expressed as the rate of exchange between current and future dollars. For example, a nominal
interest rate of 8% on a one
year loan means that $1.08

must be repaid in one year for $1.00
loaned today. But what really matters to both parties to a loan agreement is the real interest
rate, the rate at which current goods are being converted into future goods.

Looked at one way, the real rate of interest i
s the net increase in wealth that people expect to
achieve when they save and invest their current income. Alternatively, it can be viewed as
the added future consumption promised by a corporate borrower to a lender in return for the
latter's deferring cur
rent consumption. From the company's standpoint, this exchange is
worthwhile as long as it can find suitably productive investments.

However, because virtually all financial contracts are stated in nominal terms, the real
interest rate must be adjusted to
reflect expected inflation. The
Fisher effect (FE)

states that
the nominal interest rate

is made up of two components: (1) a real required rate of return

and (2) an inflation premium equal to the expected amount of inflation

Formally, the Fisher
ect is

Equation 4.11

is often approximated by the equation





The Fisher equation says, for example, that if the required real return is 3% and expected
inflation is 10%, then the nominal interest rate will be about 13% (13.3%, to be exact). The
logic behind this result is that $1 next year will have the purchasing p
ower of $0.90 in terms
of today's dollars. Thus, the borrower must pay the lender $0.103 to compensate for the
erosion in the purchasing power of the $1.03 in principal and interest payments, in addition
to the $0.03 necessary to provide a 3% real return.


Brazilians Shun Negative Real
Interest Rates on Savings

In 1981, the Brazilian government spent $10 million on an advertising campaign to help
boost national savings, which dropped sharply in 1980. According to the
Wall Street


12, 1981, p. 23), the decline in savings occurred “because the pre
rates on savings deposits and treasury bills for 1980 were far below the rate of inflation,
currently 110%.” Clearly, the Brazilians were not interested in investing money at interes
rates less than the inflation rate.

The generalized version of the Fisher effect asserts that real returns are equalized across
countries through arbitrage

that is,



where the subscripts


refer to home and
foreign real rates, respectively. If expected real returns were higher in one currency than
another, capital would flow from the second to the first currency. This process of arbitrage
would continue, in the absence of government interve
ntion, until expected real returns were

In equilibrium, then, with no government interference, it should follow that the nominal
interest rate differential

will approximately equal the anticipated inflation differential
between the two currencie
s, or



are the nominal home and foreign currency interest rates, respectively. The
exact form of this relationship is expressed by
Equation 4.13

In effect, the generalized version of the Fisher effect says that
currencies with high rat
es of
inflation should bear higher interest rates than currencies with lower rates of inflation.

For example, if inflation rates in the United States and the United Kingdom are 4% and 7%,
respectively, the Fisher effect says that nominal interest rates sho
uld be about 3% higher in
the United Kingdom than in the United States. A graph of
Equation 4.12

is shown in
. The horizontal axis shows the expected difference in inflation rates between the home
country and the foreign country, and the vertica
l axis shows the interest differential between
the two countries for the same time period. The parity line shows all points for which

Point C, for example, is a position of equilibrium because the 2% higher rate of inflation in
the foreign country



2%) is just offset by the 2% lower HC interest rate (r




At point D, however, where the real rate of return in the home country is 1% lower than in
the foreign country (an inflation differential of 2% versus an interest differential of 3%),
funds should flow from the home country to the foreign country to take advantage of the real
differential. This flow will continue until expected real returns are again equal.

Empirical Evidence

Exhibit 4.9

illustrates the relationship between interest rat
es and inflation rates for 28
countries as of May 2007. It is evident from the graph that nations with higher inflation
rates generally have higher interest rates. Thus, the empirical evidence is consistent with
the hypothesis that most of the variation in

nominal interest rates across countries can be
attributed to differences in inflationary expectations.

Exhibit 4.8.

The Fisher effect

The proposition that expected real returns are equal between countries cannot be tested
directly. However, many observ
ers believe it unlikely that significant real interest
differentials could long survive in the increasingly internationalized capital markets. Most
market participants agree that arbitrage, via the huge pool of liquid capital that operates in

markets these days, is forcing pretax real interest rates to converge across all
the major nations.

To the extent that arbitrage is permitted to operate unhindered, capital markets are
integrated worldwide.
Capital market integration

means that real interest rates are
determined by the global supply and global demand for funds. This is in contrast to
market segmentation,

whereby real interest rates are determined by local credit
conditions. The difference between capital marke
t segmentation and capital market
integration is depicted in
Exhibit 4.10
. With a segmented capital market, the real interest
rate in the United States,

is based on the national demand

and national supply

credit. Conversely, the real rate in the rest of the world,

is based on the rest

and demand D
. In this example, the U.S. real rate is higher than the real rate
outside the United States, or




Once the U.S. market ope
ns up, the U.S. real interest rate falls (and the rest
world rate
rises) to the new world rate

which is determined by the world supply



world demand



for credit. The mechanism whereby equilibrium is brought
about is a

capital inflow to the United States. It is this same capital flow that drives up the
real interest rate outside the United States.

Exhibit 4.9.

Fisher Effect: Nominal Interest Rate versus
Inflation Rate for 28 Developed and Developing Countries as
of No
vember 2007

Inflation = Change in 2007 Consumer Price

Nominal Rate = 3
Month Money Market Rate

Source: The Economist, May

17, 2007.

As shown by
Exhibit 4.10
, in an integrated capital market, the domestic real interest rate
depends on what is happening outside as well as inside the United States. For example, a
rise in the demand for capital by German companies to finance investments in Eastern
Europe will rai
se the real interest rate in the United States as well as in Germany. Similarly,
a rise in the U.S. savings rate, other things being equal, will lower the real cost of capital
both in the United States and in the rest of the world. Conversely, a fall in U.
S. inflation
will lower the nominal U.S. interest rate (the Fisher effect), while leaving unchanged real
interest rates worldwide.

Capital market integration has homogenized markets around the world, eroding much

though not all

of the real interest rate di
fferentials between comparable domestic and
offshore securities, and strengthening the link between assets that are denominated in
different currencies but carry similar credit risks.

To the extent that real interest
differentials do exist, they must be d
ue to either currency risk or some form of political

Exhibit 4.10.

The Distinction Between Capital Market
Integration and Capital Market Segmentation

A real interest rate differential could exist without being arbitraged away if investors

preferred to hold domestic assets in order to avoid currency risk, even if the
expected real return on foreign assets were higher. The evidence on this point is somewhat
mixed. The data indicate a tendency toward convergence in real interest rates
tionally, indicating that arbitrage does occur, but real rates still appear to differ from
each other.

Moreover, the estimated currency risk premium appears to be highly variable
and unpredictable, leading to extended periods of apparent differences in re
al interest rates
between nations.

These differences are displayed in
Exhibit 4.11
, which compares real interest rates
(measured as the nominal interest rate minus the past year's inflation rate as a surrogate for
the expected inflation rate) as of May 2
007 versus nominal rates for the same 28 countries
shown in
Exhibit 4.9
. According to this exhibit, countries with higher nominal interest rates
(implying higher expected inflation and greater currency risk) tend to have higher real
interest rates, resulti
ng in large real rate differentials among some countries.

In addition to currency and inflation risk, real interest rate differentials in a closely
integrated world economy can stem from countries pursuing sharply differing tax policies
or imposing regulat
ory barriers to the free flow of capital.

Exhibit 4.11.

Real Interest Rate versus Nominal Interest
Rate for 28 Developed and Developing Countries as of May

Inflation = Change in 2007 Consumer Price

Nominal Rate = 3
Month Money Market Rate

Source: T
he Economist,

May 17, 2007.


France Segments Its Capital Market

Throughout the European Monetary System's September 1992 crisis, the French franc
managed to stay within the ERM.
Exhibit 4.12

suggests why. It plots two interest rate
differentials: (1) the gap between three
month domestic money market rates and the
corresponding Eurofranc rate, which is the rate on francs deposited in London in the
Eurocurrency market (to be discussed in
r 13
) and (2) the gap between the
domestic money market rate and the bank prime rate.

France supposedly has ended capital market controls, so arbitrage should ensure that the
first of these interest differentials (shown by the solid black line) should be
pproximately zero

as it was until the crisis that began in mid
September. Once trouble
began, however, the Euromarket rate exceeded the domestic rate by a big margin for
almost two weeks, indicating that the French government was impeding the flow of
al out of France.

The other series sheds more light on what was going on during this period. Until
pressures began building in the spring, the prime lending rate slightly exceeded the
money market rate

as you might expect because money market rates help de
termine the
banks’ cost of funds. In May, however, the money market rates rose above the prime
lending rate, widening to more than 4 percentage points at the height of the crisis.

Exhibit 4.12.

France Segments Its Money Market to Defend
the Franc

The ob
vious conclusion is that the French government was using high money market
rates to defend the franc, while forcing banks to lend money at a loss in order to avoid the
adverse impact of high interest rates on the French economy.

In many developing countrie
s, however, currency controls and other government policies
impose political risk on foreign investors. In effect, political risk can drive a wedge
between the returns available to domestic investors and those available to foreign investors.
For example, i
f political risk in Brazil causes foreign investors to demand a 7% higher
interest rate than they demand elsewhere, then foreign investors would consider a 10%
expected real return in Brazil to be equivalent to a 3% expected real return in the United
s. Hence, real interest rates in developing countries can exceed those in developed
countries without presenting attractive arbitrage opportunities to foreign investors. The
combination of a relative shortage of capital and high political risk in most deve
countries is likely to cause real interest rates in these countries to exceed real interest rates
in the developed countries. Indeed, the countries in
Exhibit 4.11

with the highest real rates
of interest tend to be developing countries.

Investors’ t
olerance of economic mismanagement in developed nations also has fallen
dramatically, as financial deregulation, abolition of foreign exchange controls, and the
process of global portfolio diversification have swollen the volume of international capital
ows. With modern technology enabling investors to move capital from one market to
another at low cost and almost instantaneously, the pressure on central banks to seem to
“do the right thing” is intense. Conversely, those nations that must attract a
portionate amount of global capital to finance their national debts and that have no
credible policies to deal with their problems in a noninflationary way will be forced to pay
a rising risk premium. “Canada's High Real Interest Rate Comes Down” provides
a good
example of both these trends.


Canada's High Real Interest Rate Comes

In early 1995, the Canadian dollar slipped to an 8
year low against the U.S. dollar. At
the same time, with Canada's inflation rate under 1% and its 10
year g
overnment bonds
yielding 9.3% (about 1.5 percentage points more than 10
year U.S. Treasury bonds),
Canada had the highest real long
term interest rates in the world. The weak Canadian
dollar and high real interest rates stemmed from the same source

a lack
of confidence in
Canada's longer
term inflation prospects.

Canada had a large current
account deficit, driven by large budget deficits, political
uncertainty, and other structural problems that led to investor worries that the current low
rate of inflation

was only temporary. The persistently high budget deficits, in turn,
reflected big spending on generous social welfare programs and overly rigid labor
markets, along with a lack of political will to attack these problems. At the same time,
investors feared

that the government would rely more on tax increases than on spending
cuts to reduce the deficit. Further increases in the already high Canadian tax rates would
likely drive more of the economy underground and aggravate capital flight. Investors
were conc
erned that if higher tax rates did not reduce the deficit, and the government
would not cut spending, Canada might be tempted at some point to monetize its deficits,
reigniting inflation.

Adding fuel to these fears was the resignation of John Crow, the hig
hly respected head of
the Bank of Canada, Canada's central bank, and a strong advocate of price stability. Some
analysts contended he was forced out by government officials who opposed his tough
inflation targets. His successor as head of the Bank of C
anada followed a relatively
lax monetary policy. Investors responded to these worries by driving down the value of
the Canadian dollar and by demanding higher interest rates. In the background was the
present fear that Quebec separatists would manage
to secede from Canada.

By late 1995, Quebecs separatists had lost their referendum for independence; the federal
and provincial governments began slashing their budget deficits and planned even bigger
cuts in the future; and Canada's largest province, Onta
rio, announced large tax cuts as
well. Perceived political risk declined, and investors began focusing on Canada's low
inflation rate. As a result of these favorable trends, the Canadian dollar strengthened and,
in early 1996, short
term Canadian interest
rates fell below U.S. rates, after having stayed
above U.S. rates for more than a decade. But the yield on 10
year Canadian government
bonds stayed about 1 percentage point above that on U.S. Treasuries. With continued low
inflation, however, by late 1997,

Canada paid about 0.5 percentage points

for 10
money than did the United States.

Before we move to the next parity condition, a caveat is in order. We must keep in mind
that there are numerous interest differentials just as there are many
different interest rates in
a market. The rate on bank deposits, for instance, will not be identical to that on Treasury
bills. In computation of an interest differential, therefore, the securities on which this
differential is based must be of identical r
isk characteristics save for currency risk.
Otherwise, there is the danger of comparing apples with oranges (or at least temple oranges
with navel oranges).

Adding Up Capital Markets Internationally.

Central to understanding how we can add yen
and euro and

dollar capital markets together is to recognize that money is only a veil: All
financial transactions, no matter how complex, ultimately involve exchanges of goods
today for goods in the future. As we will see in
Chapter 5
, you supply credit (capital) whe
you consume less than you produce; you demand credit when you consume more than you
produce. Thus, the supply of credit can be thought of as the excess supply of goods and the
demand for credit as the excess demand for goods. When we add up the capital m
around the world, we are adding up the excess demands for goods and the excess supplies
of goods. A car is still a car, whether it is valued in yen or dollars.


Equation 4.13

can be converted into
Equation 4.12

by subtracting 1 from both
sides and

assuming that


are relatively small.


The net gain from the transfer of capital equals the higher returns on the capital
imported to the United States less the lower returns forgone in the rest of the world.
Returns on capital must be higher in

the United States prior to the capital inflow because
the demand for capital depends on the expected return on capital. Thus, a higher real
interest rate indicates a higher real return on capital.


An offshore security is one denominated in the home
currency but issued abroad.
They are generally referred to as Eurosecurities.


See, for example, Frederick S. Mishkin, “Are Real Interest Rates Equal Across
Countries? An International Investigation of Parity Conditions,”
Journal of Finance,

December 198
4, pp. 1345

1357. He finds that although capital markets may be
integrated, real interest rates appear to differ across countries because of currency risk.
His findings are consistent with those of Baghar Modjtahedi, “Dynamics of Real Interest
Rate Differe
ntials: An Empirical Investigation,”
European Economic Review,

32, no. 6
(1988): 1191


Adrian Throop, “International Financial Market Integration and Linkages of
National Interest Rates,”
Federal Reserve Bank of San Francisco Economic Review,

(1994): 3
18, found that exchange risk caused persistent real interest rate differentials
among developed nations for the years 1981 to 1993.


The International Fisher Effect

The key to understanding the impact of relative changes in nominal interest

rates among
countries on the foreign exchange value of a nation's currency is to recall the implications of
PPP and the generalized Fisher effect. PPP implies that exchange rates will move to offset
changes in inflation rate differentials. Thus, a rise in

the U.S. inflation rate relative to those of
other countries will be associated with a fall in the dollar's value. It will also be associated
with a rise in the U.S. interest rate relative to foreign interest rates. Combine these two
conditions and the re
sult is the
international Fisher effect (IFE):


is the expected exchange rate in period t. The single
period analogue to


According to
Equation 4.15
, the expected return from investing at home, 1 +

should equal
the expected HC return from investing abroad,
. As discussed in the
previous section, however, despite the intuitive appeal of equal expected returns, domestic
and foreign expected returns might not equilibrate if the element of currency ris
k restrained
the process of international arbitrage.


Using the IFE to Forecast U.S.$ and
SFr Rates

In July, the one
year interest rate is 2% on Swiss francs and 7% on U.S. dollars.


If the current exchange rate is SFr 1 = $0.91, what is the
expected future exchange
rate in one year?


According to the international Fisher effect, the spot exchange rate expected in
one year equals 0.91 × 1.07/1.02 = $0.9546


If a change in expectations regarding future U.S. inflation causes the expec
future spot rate to rise to $1.00, what should happen to the U.S. interest rate?



is the unknown U.S. interest rate, and the Swiss interest rate stayed at 4%
(because there has been no change in expectations of Swiss inflation), then ac
cording to
the international Fisher effect, 1.00/0.91 = (1 + r
)/1.2, or

= 11.21%.


is relatively small,
Equation 4.16

provides a reasonable approximation to the
international Fisher effect:

In effect, the IFE says that
currencies with low
interest rates are expected to appreciate
relative to currencies with high interest rates.

A graph of
Equation 4.16

is shown in
Exhibit 4.13
. The vertical axis shows the expected
change in the home currency value of the foreign currency, and the horizontal

axis shows the
interest differential between the two countries for the same time period. The parity line
shows all points for which

Point E is a position of equilibrium because it lies on the parity line, with the 4% interest
differential in favor of th
e home country just offset by the anticipated 4% appreciation in the
HC value of the foreign currency. Point F, however, illustrates a situation of disequilibrium.
If the foreign currency is expected to appreciate by 3% in terms of the HC, but the interest

differential in favor of the home country is only 2%, then funds would flow from the home to
the foreign country to take advantage of the higher exchange
adjusted returns there. This
capital flow will continue until exchange
adjusted returns are equal in
the two nations.

Exhibit 4.13.

International Fisher Effect


Subtracting 1 from both sides of
Equation 4.15


Equation 4.16

follows if

is relatively small.

Essentially what the IFE says is that arbitrage between financial markets

in the form of
international capital flows

should ensure that the interest differential between any two
countries is an
unbiased predictor

of the future change in the spot rate of ex
change. This
condition does not mean, however, that the interest differential is an especially accurate
predictor; it just means that prediction errors tend to cancel out over time. Moreover, an
implicit assumption that underlies IFE is that investors view

foreign and domestic assets as
perfect substitutes. To the extent that this condition is violated (see the discussion on the
Fisher effect, p. 158) and investors require a risk premium (in the form of a higher expected
real return) to hold foreign assets,

IFE will not hold exactly.

Empirical Evidence

As predicted, there is a clear tendency for currencies with high interest rates (e.g., in
Mexico and Brazil) to depreciate and those with low interest rates (e.g., in Japan and
Switzerland) to appreciate. The
ability of interest differentials to anticipate currency
changes is supported by several empirical studies that indicate the long
run tendency for
these differentials to offset exchange rate changes.

The international Fisher effect also
appears to hold e
ven in the short run in the case of nations facing very rapid rates of
inflation. Thus, at any given time, currencies bearing higher nominal interest rates can be
reasonably expected to depreciate relative to currencies bearing lower interest rates.

e this apparently convincing evidence for the international Fisher effect, a large body
of empirical evidence now indicates that the IFE does not hold up very well in the short run
for nations with low to moderate rates of inflation.

One possible explana
tion for this
result relies on the existence of a time
varying exchange risk premium. However, this
explanation for the failure of the IFE to hold in the short run has been challenged by
empirical evidence indicating that the currency risk premium, to the
extent it exists, is very

A more plausible explanation for the IFE's failure in the short run relies on the nature of the
Fisher effect. According to the Fisher effect, changes in the nominal interest differential
can result from changes in either

the real interest differential or relative inflationary
expectations. These two possibilities have opposite effects on currency values. For
example, suppose that the nominal interest differential widens in favor of the United States.
If this spread is due

to a rise in the real interest rate in the United States relative to that of
other countries, the value of the dollar will rise. Alternatively, if the change in the nominal
interest differential is caused by an increase in inflationary expectations for th
e United
States, the dollar's value will drop.

The key to understanding short
run changes in the value of the dollar or other currency,
then, is to distinguish changes in nominal interest rate differentials that are caused by
changes in real interest rate
differentials from those caused by changes in relative inflation
expectations. Historically, changes in the nominal interest differential have been
dominated, at times, by changes in the real interest differential; at other times, they have
been dominated
by changes in relative inflation expectations. Consequently, there is no
stable, predictable relationship between changes in the nominal interest differential and
exchange rate changes.

It is also possible that capital movements to take advantage of intere
st rate differentials can
be driving exchange rates in the opposite direction to that predicted by the IFE. One
example of this phenomenon is the carry trade, whose existence also indicates that many
investors believe that they can profitably arbitrage int
erest rate differentials across
countries on an unhedged (or “uncovered”) basis.


The Carry Trade

carry trade

involves borrowing a currency bearing a low interest rate and investing
the proceeds in a currency bearing a high interest rate. In recent years, the carry trade has
centered on borrowing yen in Japan at rates close to zero and selling the yen to invest i
yielding assets, such as U.S. Treasury notes or European bonds. By 2007, it was
estimated that the yen carry trade totaled about $1 trillion. According to the international
Fisher effect, carry trades should not yield a predictable profit because
the interest rate
differential between two currencies should (aside from currency risk considerations)
equal the rate at which investors expect the low interest rate currency to appreciate
against the high interest rate one. However, the existence of a lar
ge volume of carry
trades may lead to an opposite result. For example, as borrowed yen are sold to buy
dollars, carry trades will send the yen lower and boost the dollar.

The danger, of course, is that the small, steady returns from the carry trade (say,
orrowing at 1% in yen and investing at 5% in dollars to earn a spread of 4%) is the
possibility of a very large, very sudden loss when the dollar sinks or the yen jumps in
value. The currency effect will be exacerbated if speculators try to cut their losse
s by
bailing out of their dollar assets and repaying their yen debts. This risk is captured in the
colorful description of the carry trade as “picking up nickels in front of a steamroller.”

A good example of this occurred in 2007 when the Federal Reserve s
tarted slashing
term interest rates in September. With Japans rates remaining unchanged, the yen
jumped sharply against the dollar. In response, many carry trade speculators unwound
their carry trades, helping to push the yen up further and triggerin
g a global sell
off in
assets that had been financed by the yen carry trade.


Interest Rate Parity Theory

Spot and forward rates are closely linked to each other and to interest rates in different
currencies through the medium of arbitrage. Specificall
y, the movement of funds between
two currencies to take advantage of
interest rate differentials

is a major determinant of the
spread between forward and spot rates. In fact, the forward discount or premium is closely
related to the interest differential b
etween the two currencies.

According to
interest rate parity (IRP)

theory, the currency of the country with a lower
interest rate should be at a forward premium in terms of the currency of the country with the
higher rate. More specifically, in an efficien
t market with no transaction costs, the interest
differential should be (approximately) equal to the forward differential. When this condition
is met, the forward rate is said to be at interest rate parity, and equilibrium prevails in the
money markets.

terest parity ensures that the return on a hedged (or “covered”) foreign investment will just
equal the domestic interest rate on investments of identical risk, thereby eliminating the
possibility of having a money machine. When this condition holds, the
overed interest

the difference between the domestic interest rate and the hedged foreign rate

is zero. To illustrate this condition, suppose an investor with $1,000,000 to invest for 90 days
is trying to decide between investing in U.S. dollar
s at 8% per annum (2% for 90 days) or in
euros at 6% per annum (1.5% for 90 days). The current spot rate is

0.74000/$, and the 90
day forward rate is

Exhibit 4.14

shows that regardless of the investors currency
choice, his hedged return will
be identical. Specifically, $1,000,000 invested in dollars for 90
days will yield $1,000,000 × 1.02 = $1,020,000. Alternatively, if the investor chooses to
invest in euros on a hedged basis, he will


Convert the $1,000,000 to euros at the spot rate of

.740000/$. This yields

740,000 available for investment.


Invest the principal of

740,000 at 1.5% for 90 days. At the end of 90 days, the
investor will have



Simultaneously with the other transactions, sell the

751,100 in principal plus
interest forward at a rate of

0.73637/$ for delivery in 90 days. This transaction will yield

751,100/0.73637 = $1,020,000 in 90 days.

Exhibit 4.14.

An example of interest rate PaRITY


Covered Interest Arbitrage Bet
ween London
and New York

Suppose the interest rate on pounds sterling is 12% in London, and the interest rate on a
comparable dollar investment in New York is 7%. The pound spot rate is $1.95, and the
year forward rate is $1.87. These rates imply a f
orward discount on sterling of 4.10%
[(1.87 − 1.95)/1.95] and a covered yield on sterling approximately equal to 8% (12% −
4%). Because there is a covered interest differential in favor of London, funds will flow
from New York to London.

To illustrate the profits associated with covered interest arbitrage, we will assume that the
borrowing and lending rates are identical and the bid
ask spread in the spot and forward
markets is zero. Here are the steps the arbitrageur can take to profit fr
om the discrepancy in
rates based on a $1,000,000 transaction. Specifically, as shown in
Exhibit 4.15
, the
arbitrageur will


Borrow $1,000,000 in New York at an interest rate of 7%. This means that at the
end of one year, the arbitrageur must repay princ
ipal plus interest of $1,070,000.


Immediately convert the $1,000,000 to pounds at the spot rate of £1 = $1.95. This
yields £512,820.51 available for investment.


Invest the principal of £512,820.51 in London at 12% for one year. At the end of
the year
, the arbitrageur will have £574,358.97.


Simultaneously with the other transactions, sell the £574,358.97 in principal plus
interest forward at a rate of £1 = $1.87 for delivery in one year. This transaction will
yield $1,074,051.28 next year.


At the

end of the year, collect the £574,358.97, deliver it to the bank's foreign
exchange department in return for $1,074,051.28, and use $1,070,000 to repay the loan.
The arbitrageur will earn $4,051.28 on this set of transactions.

Exhibit 4.15.

An example of

covered interest arbitrage

If the covered interest differential between two money markets is nonzero, there is an
arbitrage incentive to move money from one market to the other. This movement of money to
take advantage of a covered interest differential

is known as
covered interest arbitrage.

The transactions associated with covered interest arbitrage will affect prices in both the
money and foreign exchange markets. In the previous example, as pounds are bought spot
and sold forward, boosting the spot r
ate and lowering the forward rate, the forward discount
will tend to widen. Simultaneously, as money flows from New York, interest rates there will
tend to increase; at the same time, the inflow of funds to London will depress interest rates
there. The pro
cess of covered interest arbitrage will continue until interest parity is achieved,
unless there is government interference.

If this process is interfered with, covered interest differentials between national money
markets will not be arbitraged away. Inte
rference often occurs because many governments
regulate and restrict flows of capital across their borders. Moreover, just the risk of controls
will be sufficient to yield prolonged deviations from interest rate parity.

The relationship between the spot an
d forward rates and interest rates in a free market can be
shown graphically, as in
Exhibit 4.16
. Plotted on the vertical axis is the interest differential in
favor of the home country. The horizontal axis plots the percentage forward premium
(positive) or

discount (negative) on the foreign currency relative to the home currency. The
interest parity line joins those points for which the forward exchange rate is in equilibrium
with the interest differential. For example, if the interest differential in favor

of the foreign
country is 2%, the currency of that country must be selling at a 2% forward discount for
equilibrium to exist.

Exhibit 4.16.

Interest Rate Parity Theory

Point G indicates a situation of disequilibrium. Here, the interest differential is
2%, whereas
the forward premium on the foreign currency is 3%. The transfer of funds abroad with
exchange risks covered will yield an additional 1% annually. At point H, the forward
premium remains at 3%, but the interest differential increases to 4%. Now
reversing the flow
of funds becomes profitable. The 4% higher interest rate more than makes up for the 3% loss
on the forward exchange transaction, leading to a 1% increase in the interest yield.

In reality, the interest parity line is a band because trans
action costs, arising from the spread
on spot and forward contracts and brokerage fees on security purchases and sales, cause
effective yields to be lower than nominal yields. For example, if transaction costs are 0.75%,
a covered yield differential of onl
y 0.5% will not be sufficient to induce a flow of funds. For
interest arbitrage to occur, the covered differential must exceed the transaction costs

The covered interest arbitrage relationship can be stated formally. Let

be the current spot
te (dollar value of one unit of foreign currency) and

the end
period forward rate. If


are the prevailing interest rates in New York and, say, London, respectively, then one
dollar invested in New York will yield 1 +

at the end of the per
iod; the same dollar
invested in London will be worth (1 +

dollars at maturity. This latter result can be
seen as follows: One dollar will convert into 1/e

pounds that, when invested at

will yield
(1 +

pounds at the end of the period.
By selling the proceeds forward today, this amount
will be worth (1 +

dollars when the investment matures.

Funds will flow from New York to London if and only if

Conversely, funds will flow from London to New York if and only if

Interest rate

holds when there are no covered interest arbitrage opportunities. On the
basis of the previous discussion, this no
arbitrage condition can be stated as follows:


Using Interest Rate Parity to Calculate the $/¥
Forward Rate

The interest

rate in the United States is 10%; in Japan, the comparable rate is 7%. The spot
rate for the yen is $0.003800. If interest rate parity holds, what is the 90
day forward rate?


According to IRP, the 90
day forward rate on the yen, f
, should be

In other words, the 90
day forward Japanese yen should be selling at an annualized
premium of about 2.95% [4 X (0.003828 − 0.003800)/0.0038].

Interest rate parity is often approximated by
Equation 4.18

In effect, interest rate parity says

high interest rates on a currency are offset by forward
discounts and that low interest rates are offset by forward premiums.

Transaction costs in the form of bid
ask spreads make the computations more difficult, but
the principle is the same: Comput
e the covered interest differential to see whether there is an
arbitrage opportunity.


Computing the Covered Interest
Differential When Transaction Costs Exist

Suppose the annualized interest rate on 180
day dollar deposits is 6 7/16 − 5/16%, m
that dollars can be borrowed at 6 7/16% (the ask rate) and lent at 6 5/16% (the bid rate). At
the same time, the annualized interest rate on 180
day Thai baht deposits is 9 3/8 − 1/8%.
Spot and 180
day forward quotes on Thai baht are B 31.5107 − 46/
$ and B 32.1027 − 87/$,
respectively. Is there an arbitrage opportunity? Compute the profit using B 10,000,000.


The only way to determine whether an arbitrage opportunity exists is to examine
the two possibilities: Borrow dollars and lend Thai baht or borrow baht and lend dollars,
both on a hedged basis. The key is to ensure that you are using the correct bid or as
interest and exchange rates. In this case, it turns out that there is an arbitrage opportunity
from borrowing Thai baht and lending dollars. The specific steps to implement this
arbitrage are as follows:


Borrow B 10,000,000 at the ask rate of 9 3/8% f
or 180 days. This interest rate
translates into a 180
day rate of 0.09375/2 = 4.6875%, requiring repayment of B
10,468,750 in principal plus interest at the end of 180 days.


Immediately convert the B 10,000,000 to dollars at the spot ask rate of B
46/$ (the baht cost of buymg dollars spot). This yields $317,313.25
($10,000,000/31.5146) available for investment.


Invest the principal of $317,313.25 at 0.063125/2 = 3.15625% for 180 days. In six
months, this investment will have grown to $327,328.44
($317,313.25 × 1.0315625).


Simultaneously with the other transactions, sell the $327,328.44 in principal plus
interest forward at the bid rate of B 32.1027 (the rate at which dollars can be converted
into baht) for delivery in 180 days. This transaction

will yield B 10,508,126.86 in 180


At the end of six months, collect the $327,328.44, deliver it to the bank's foreign
exchange department in return for B 10,508.126.86, and use B 10,468,750 of the
proceeds to repay the loan. The gain on this set
of transactions is B 39,376.86.

Empirical Evidence

Interest rate parity is one of the best
documented relationships in international finance. In
fact, in the Eurocurrency markets, the forward rate is calculated from the interest
differential between the two currencies using the no
arbitrage condition. Devi
ations from
interest parity do occur between national capital markets, however, owing to capital
controls (or the threat of them), the imposition of taxes on interest payments to foreigners,
and transaction costs. However, as we can see in
Exhibit 4.17
, th
ese deviations tend to be
small and short

Exhibit 4.17.

Uncovered and Covered Interest Rate
Differentials (U.S. $ versus Other Currencies)


Bhar, Buk
Joogn, Kim. Ramprasad, and Toan M., Pham, “Exchange Rate
Volatility and Its Impact on the

Transaction Cost of Covered Interest Rate Parity.”
Japan and the World Economy,

Vol. 16, 2004.


See, for example, Ian H. Giddy and Gunter Dufey, “The Random Behavior of
Flexible Exchange Rates,”
Journal of International Business Studies,

Spring 1975, p
p. 1
32; and Robert A. Aliber and Clyde P. Stickney, “Accounting Measures of Foreign
Exchange Exposure: The Long and Short of It,”
The Accounting Review,

January 1975,
pp. 44


Much of this research is summarized in Kenneth A. Froot, “Short Rates and

Expected Asset Returns,” NBER Working Paper No. 3247, January 1990.


See, for example, Kenneth A. Froot and Jeffrey A. Frankel, “Forward Discount
Bias: Is It an Exchange Risk Premium?”
Quarterly Journal of Economics,

February 1989,
pp. 139


tracting 1 from both sides of
Equation 4.17

yields (f − e

= (r

rf)/(1 +


Equation 4.18

follows if

is relatively small.


The Relationship Between the Forward Rate and the
Future Spot Rate

Our current understanding of the workings of the
foreign exchange market suggests that in
the absence of government intervention in the market, both the spot rate and the forward rate
are influenced heavily by current expectations of future events. The two rates move in
tandem, with the link between them

based on interest differentials. New information, such as
a change in interest rate differentials, is reflected almost immediately in both spot and
forward rates.

Suppose a depreciation of the pound sterling is anticipated. Recipients of sterling will beg
selling sterling forward, and sterling
area dollar earners will slow their sales of dollars in the
forward market. These actions will tend to depress the price of forward sterling. At the same
time, banks will probably try to even out their long (net pu
rchaser) positions in forward
sterling by selling sterling spot. In addition, sterling
area recipients of dollars will tend to
delay converting dollars into sterling, and earners of sterling will speed up their collection
and conversion of sterling. In thi
s way, pressure from the forward market is transmitted to the
spot market, and vice versa.

Ignoring risk for the moment, equilibrium is achieved only when the forward differential
equals the expected change in the exchange rate. At this point, there is no
longer any
incentive to buy or sell the currency forward. This condition is illustrated in
Exhibit 4.18
The vertical axis measures the expected change in the home currency value of the foreign
currency, and the horizontal axis shows the forward premium or

discount on the foreign
currency. Parity prevails at point I, where the expected foreign currency depreciation of 2%
is just matched by the 2% forward discount on the foreign currency. Point J, however, is a
position of disequilibrium because the expected

4% depreciation of the foreign currency
exceeds the 3% forward discount on the foreign currency. We would, therefore, expect to see
speculators selling the foreign currency forward for home currency, taking a 3% discount in
the expectation of covering the
ir commitment with 4% fewer units of HC.

Exhibit 4.18.

Relationship Between the Forward Rate and
the Future Spot Rate

A formal statement of the
unbiased forward rate (UFR)

condition is that the forward rate
should reflect the expected future spot rate on the date of settlement of the forward contract:


is the expected future exchange rate at time

(units of home currency per unit of
foreign currency) and

is th
e forward rate for settlement at time


Using UFR to Forecast the Future $/