Did Steroid Use Enhance the Performance of the Mitchell Batters? The Effect of Alleged Performance Enhancing Drug Use on Offensive Performance from 1995 to 2007

Introduction: The Mitchell Report to the Commissioner of Baseball sought to characterize the extent to which the use of performance enhancing drugs (PEDs) proliferated through baseball during the last 15 years. While the Report was not primarily initiated to expose individual players, it nonetheless contained detailed accounts of alleged PED abuse by 89 current and former players including seasons in which the abuse occurred and type of abuse (steroids or human growth hormone (HGH)). Previous analyses have largely focused on the impact of PED abuse on individual players (Barry Bonds and Roger Clemens, for instance). The present study integrates data from the Mitchell Report to make inferences about the overall effects of PED abuse on offensive production.Methods: The Lahman database was queried for all offensive seasons from 1995 to 2007 (minimum 50 PA, no pitchers). Runs created per 27 outs (RC27) was used as an estimate of the offensive production of a player in a season. An adjusted RC27 (ADJRC27) was obtained by accounting for career progression effects to reduce the influence of the expected change in performance over time due to age. Information from the Mitchell Report identified each player season as a PED season or a non-PED season. General linear mixed effects models were constructed that modeled ADJRC27 as a function of PED use (Yes or No). Multiple models were considered to assess the PED effect under various assumptions.Results: The baseline model estimated a mean non-steroid ADJRC27 during the study period of 4.58. The effect of steroid use was an additional 0.58 ADJRC27, an increase in production of 12.6% (p=0.0108). Additional models considered the effect of being a player mentioned in the Mitchell Report, adjustments for baseline performance, and the influential effect of Barry Bonds' performance. The estimated steroid effect ranged from 3.9% to 18.0% among twelve different models. Similar analysis of HGH use showed no evidence of performance improvement.Conclusions: This analysis suggests a significant and substantial performance advantage for players who used steroids during the study period. It is estimated that offensive production increased approximately 12% in steroid users versus non-users. This analysis represents the first attempt to quantify the overall effect of PED abuse on offensive performance in baseball.