ABSTRACT
Differentiating equation (9) with respect to an independent variable (x) in county k in year t gives (Greene, p. 697)
(10) dsikt/d x b — + X j Sih
i = 1, . . . , 6
where (3 ^ is the coefficient of x in equation i. Thus, the acreage elasticity of crop i with respect to x in county k in year t is
(ID M* xk, dxb n *
dxb s ’m
The independent variables other than dummy and time variables used in the acreage response models are listed in the first column of table 1. Using central Wisconsin as a reference region, a dummy variable is used for each of the other regions listed in the first column of table 3 to capture the regional difference in Wisconsin. In addition, a time variable (r = 1 for 1972, . . . , 19 for 1990) is used to reflect technological progress and other trends in the study period. The price and policy variables are based only on time-series data (without any variability across counties), while the site characteristics, population density, and dummy variables are cross-sectional. Observations on crop acreage and the number of cows are from pooled cross-sectional and time-series data.
