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

had statistical significance; however, they were all much lower in
value than in the supply equations and three of the significant es-
timates had the wrong, or a negative, sign.
The results for grain and iron and steel products were much the
same. In the grain supply equations only two of the b 1 estimates were
significant, and one of these was of negative sign. Only one of the
b 2 estimates turned out significant in the grain import equations.
Much the same results were found in the iron and steel equations. The
only overall pattern that emerged from the equations was that the b 1
estimates fell between plus one and minus one and were not significant.
The four significant b 2 estimates ranged in value from -0.069 to -0.837.
Three significant b 2 estimates were obtained in the iron and steel im-
port equations. Again, however, the problem of signs was encountered'
with two of the estimates being positive and the other negative.
The main impression obtained from an overall view of Silberberg i s
regression results is that they represent somewhat encouraging first
approximations. The poorness of some of the results is surprising:
One would think, for example, that the larger the output of coal in a
region the greater would be the barge shipments of coal from that region.
No clearcut findings of this type came out of the analysis. Still more
disturbing are the mixed results obtained for the rate variable. On
a priori grounds one would have expected that the greater the positive
difference between the rail rate and the barge rate, the more tonnage
would move by barge. As indicated, however, the coefficient pertaining
to this variable often appeared with the wrong sign and, even when of :
the correct sign, was most often not statistically different from zero.
We suspect that many of these difficulties arose from the use of
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