The Contribution of Genetic Modification to Changes in Corn Yield in the United States

We use a large, rich dataset compiled from results of university extension trials to estimate the contribution of genetic modification (GM) to changes in corn yield in the United States from timeA to timeB. Through repeated experimental trials, we obtain consistent estimates of the effect of these traits by using both the Hausman-Taylor estimator and a comparison of fixed effects estimates analogous to the agronomic practice of comparing near-isolines. Our results suggest that GM traits had a positive impact on yield, but that gains associated with combining several GM traits in one hybrid are not necessarily additive. Copyright 2012, Oxford University Press.