A Note on the Nerlove Model of Agricultural Supply Response
指出Nerlove农业供给反应模型中存在严重的共线性问题，可能导致供给弹性估计不可靠，并提供了一个实证例子。
Judged by the number of studies which follow a particular approach more or less closely, Nerlove's famous formulation of agricultural supply response is certainly one of the most successful econometric models introduced into the literature. The surveys of Askari and Cummings [1976, 1977] provide clear evidence. Even though they are restricted to the English literature, they contain the results of well over one hundred empirical studies in the Nerlovian tradition. In examining Askari and Cummings' very helpful summary tables, one is unavoidably struck by some extreme discrepancies in long-run supply elasticities found by different researchers for the same crops and regions and almost identical observation periods. While such discrepancies may be due to different definitions of the key variables or to certain modifications of the basic model and thus to aspects which are extensively discussed by Askari and Cummings, they might alternatively reflect a serious collinearity problem that appears to be built into the Nerlove model and which may not be resolvable. It is the purpose of this note to draw attention to this apparently largely overlooked problem, briefly discuss its consequences and provide another empirical example in which the suggested collinearity may be responsible for obviously unreliable supply elasticity estimates.