Variability in regional wheat yields as a function of climate, soil and economic variables: Assessing the risk of confounding

Soft wheat productivity could be described to a very satisfying level. High R2 values were obtained, partly due to aggregation of spatially autocorrelated in- and output data. High correlations were found between all variables, which indicates a risk of misinterpretation of results from statistical models when only few (groups of) variables are considered in the analysis. At a higher aggregation level (NUTS2) both the model fit and the risk of confounding increase. Validation by an independent dataset does not lead to exclusion of confounding. This paper serves as a basis for further research on spatial variability and trends in agricultural productivity at the regional scale, indicating both the possibilities and the risks of such research.