This study uses corn yield data from McLean County, Illinois to test whether farmer skill influences yields. This analysis is conducted by performing persistency tests on unadjusted, soil productivity adjusted (PA), and productivity and input intensity adjusted (PIA) yields. Correlation analysis and winner/loser tables indicate that unadjusted, PA, and PIA yields exhibit persistency across time. PIA yields exhibiting persistency is consistent with farmer skill influencing yield. Hence, our results support the hypothesis that farmer skill influences yields.