FACTORS ASSOCIATED WITH VARIATION IN AGGREGATE AVERAGE YIELD OF NEW ZEALAND WHEAT ,1918-1967)

An apparently successful test of a “step function” hypothesis about the effect of technological change in the agricultural sector is reported. The effects of weather and other factors on wheat yields are also analyzed. A notable feature of the research was the lack of significance of an ordinary time trend variable, used as a surrogate for technological change, when a detailed specification of these factors was developed. Overall, 98.6 percent of the variance of the dependent variable in the sample was accounted for by a regression relationship involving seven weather and four non-weather variables, only one of which related to technological change. The potential value of this relationship for forecasting crop yield is indicated by the fact that the standard error of forecast was substantially less than the standard deviation of errors for the present system of pre-harvest yield estimation. © 1969, Oxford University Press.