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Price Movements and Price Discovery in Futures and Cash Markets

Author(s): Kenneth D. Garbade and William L. Silber

Reviewed work(s):

Source:

The Review of Economics and Statistics,

Vol. 65, No. 2 (May, 1983), pp. 289-297

Published by: The MIT Press

Stable URL: /stable/1924495 .

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PRICE MOVEMENTS

AND PRICE

DISCOVERY

IN

FUTURES

AND CASH

MARKETS

Kenneth D. Garbade

and William L.

Silber*

I.

Introduction

R

are two of

and price discovery

ISK transfer

the major contributions

of futures markets

to

the organization

of economic activity

(Working

(1962), Evans (1978,

p. 80), and Silber

(1981)).

Risk transfer refers to hedgers

using futures

con-

tracts to shift price

risk to others. Price

discovery

refers to the use

of futures prices for pricing

cash

market transactions

(Working (1948),

Wiese (1978,

p. 87), and Lake

(1978, p. 161)).

The significance

of both contributions

depends upon a

close rela-

tionship between the

prices of futures

contracts

and cash commodities.

This paper examines

the characteristics

of price

movements

in cash (or spot) markets

and futures

markets for storable

commodities. Section

II pre-

sents an analytical

model of simultaneous

price

dynamics

which suggests that, over short

intervals

of time, the correlation

of price changes

is a func-

tion of the elasticity

of arbitrage between

the

physical commodity

and its counterpart

futures

contract. Greater

elasticity fosters

more highly cor-

related price changes,

and thereby facilitates

the

risk transfer function.

The elasticity of supply

of

arbitrage services

is constrained by, among

other

things, storage

and transaction costs. Thus,

futures

contracts

will not, in general, provide perfect

risk

transfer facilities

over short time horizons.

The essence of the

price discovery

function of

futures markets hinges

on whether new informa-

tion is reflected

first in changed futures prices

or in

changed cash prices

(Hoffman (1932,

pp. 258-

259)). The model

in section

II

provides a frame-

work for analyzing

whether one market

is dom-

inant in terms of information

flows and price

discovery.

In section III we develop a model based

on section

II which is appropriate for estimating

the lead-lag relationship

between cash prices

and

futures prices.

Section IV presents empirical

estimates of the

parameters of the

model for seven different

stor-

able commodities: wheat, corn,

oats, frozen orange

juice concentrates, copper,

gold, and silver.

The

cost of arbitrage between

cash and futures differs

across these commodities.

For this reason we are

not surprised to find inter-commodity

differences

in the correlation of short-run

price changes and

in the substitutability of

futures contracts for cash

market positions. With

respect to the price

dis-

covery function of futures

markets, we find that

while futures markets dominate

cash markets, cash

prices do not merely

echo futures prices; there

are

reverse information flows

from cash markets

to

futures markets as well.

II.

A Model of Simultaneous

Price

Dynamics

This section sets forth

a model of concurrent

price changes in

a cash market and

a futures

market, and uses that

model to examine: (1)

the

effect of arbitrage on the

correlation of price

changes

in the two markets; and (2) the

notion of

price discovery.

We first present an equilibrium

price relationship

assuming an infinite elasticity

of

supply

of arbitrage services, and

then extend that

relationship to the case

of a finite elasticity

of

supply.

Prices with Infinitely Elastic

A.

Equilibrium

Arbitrage

Let

Ck

be the natural logarithm

of the cash

market price of a storable

commodity

in

period k,

and let

Fk

be the natural logarithm of the

contem-

poraneous price

on a futures contract for

that

commodity

for settlement after a time

interval

Tk.

(All prices

are expressed in natural logarithms.)

If

the following "perfect

market" assumptions hold:

(1) no taxes

or transaction costs; (2) no

limitations

on borrowing; (3) no costs (other

than financing)

to storing a long cash market position,

e.g.,

no

[

289

1

Received for publication

December

15, 1981. Revision

accepted for publication July

29, 1982.

* New York University.

This paper was supported

by NSF Grant No. SES-8103156

and by grants from J.

Aron & Co. and Bankers

Trust Co.

Deborah Black provided

excellent assistance,

and Mary Jaffier

typed the drafts with her

usual speed and accuracy.


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