101
(1-B)(1 .390B + .135B3)Et et
(1B)(l .466B + .093B2)Wt wfc
where Efc and are ex-vessel and wholesale price, respectively. Sub
stituting the above ARIMA expressions for et and wt into the dynamic
shock model yields the expression
(1-B)(1 .466B + .093B2)Wfc = (.651 .252B)(1-B)(1 .390B
+ ,135B3)Et + (1 B)at
which is the impulse response function. By carrying out the indicated
multiplication and division, the above expression reduces to
Wt (.651 .203B .058B2 + .078B3 + .006B4 .006B5 .015B6
- .013B7 .002B8 .001B9 .00lB10)Et + 9(B)at
where 9(B) is some polynomial on the error term at. By dropping all
terms that are small relative to the leading parameters (less than .1),
Wt can be expressed in a more parsimonious form as
Wt (.651 .203B)Et + 9(B)at
Thus, the Haugh-Pierce causality results and the impulse response func
tion derivation suggested that current wholesale price be expressed as
some function of current ex-vessel price and ex-vessel price lagged one
period. Therefore, the final specification of the price dependent
demand expression at the wholesale level for 31-40 size class raw-
headless shrimp contains current ex-vessel price of 31-40 size product
and ex-vessel price lagged one period. The derivation of the monthly
impulse response functions for the 31-40 size class retail/wholesale and
21-25 size class retail/wholesale market level interfaces are presented