Study: Steroids Enhanced Performance for Mitchell Report Players

J.C. Bradbury at Sabernomics points to a new study concluding that baseball players named in the Mitchell Report got a little production boost from using performance enhancing drugs.

Compared to the average player between the 1995 and 2007 seasons, Mitchell Report players got a performance bump of between 7 and 12 percent in the seasons that they were identified as using steroids, write Brian Schmotzer, Jeff Switchenko, and Patrick Kilgo of Emory University's School of Public Health in the study published in the Journal of Quantitative Analysis in Sports.

The effect was limited to those players who were I.D.'ed as using steroids. Exclusive use of human growth hormones had no positive impact on a player's output, a conclusion also reached in this study.

However, there is a silent elephant in the room in the name of Barry Bonds, says Bradbury. When he is kept out of the dataset, the correlation between being named in the Mitchell Report and improved performance disappears.

On the other hand, when the researchers included Bonds they only identified his 2003-04 seasons as steroid-use seasons. According to the statistic used to measure performance in the paper, runs created, the '03 and '04 seasons were Bonds' 3rd and 5th-best, respectively. Under this scenario, the link between steroids and performance for the average player was significant and came out to about 7 percent.

Two other studies have been conducted using data from the Mitchell Report. This one by statisticians at Cornell and the University of Chicago found no evidence of a steroids boost while this one by Milwuakee's Journal Sentinel found that more than half of the 90 players identified in the Mitchell Report played better in the two years after juicing. (This latter finding has also been criticized.)

Relatedly, after the first month-and-a-half of this season, there wastalk that the Steroids Era was over because offensive production had fallen off considerably.

Now that we're more than 75 percent of the way into the season, it looks like there's been some reversion to the mean. Although the slugging percentage for the entire league is at its lowest level since 1995, it's only two points below its previous low of 0.417 percent in 2002: