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.

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These findings support the utility of screening patients with IBD for psychological difficulties and estimates of QOL. Further research and group interventions are recommended.

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