Q2 Z2,(Q2) Z2(Q2) - Institute for Water Resources - U.S. Army

products, have different cost functions, and/or ship to
different markets.
• Previous work by Beuthe and Moses ' clearly demonstrates
that individual shippers of relatively homogeneous products
tend to choose one mode or another. For that study the
authors were able to obtain excellent data on shipments
of grain from hundreds of individual elevators in Illinois
to the Chicago market and to Southern markets, primarily to
New Orleans. Data on transport costs from each elevator
to these markets by rail, truck, and water were obtained
directly. Excellent price data was available on a daily
basis. It was found that more than eighty-five per cent
of all shipments involved a single mode.
Phenomena that involve exclusive choice lend them-
elves to a statistical technique known as discriminant
• analysis in which the dependent variable takes on values
of zero or one. In the grain study there was a vector
of independent variables for each shipping point, these
variables representing time, cost, etc., of shipping.
The model was able to separate the various mode populations
successfully, which is to say that it tended to correctly
• allocate shipments to the mode actually used. For the
study of air cargo demand detailed data of the above sort
was not available. It was, therefore, necessary to adjust
• the basic statistical procedure from that described in
.
Chapter III above. The data available and the required
adjustment are explained below. •
1 M.V. BeuthDand L.N. Moses, "The Demand for Transportation:
The Influence of Time", in Transportation: A Service, (New
York Academy of Sciences, New York, 1968), pp. 61-65.
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