I am sick and tired of reading about how Barry Bonds’s records, among others, are tainted due to steroids. Let’s look at Bonds’s success in his recent offensive boom. I’ll exclude his first year in the league to limit some bias to these estimates. From 1987-1999 Bonds hit .292 with a SLG of .572. From 2000-2003 these numbers rose to .336 and .774. This change has two potential causes: 1) Bonds simply became better or 2) he used steroids to become better. “The media” is very fond of the latter explanation.
There is a simple way to determine which was the cause. Steroids ought to increase a hitter’s ability to hit the ball harder. This will result in every ball he hits generating more power (i.e. outs become singles, singles become doubles, flyouts become HRs, etc.). This means both his batting average and SLG should go up with steroid use; although, I suspect the effect on batting average would be much less. But, one thing steroids should not change is Bonds’s hitting discipline, as measured by his walk rate.
In the table below I list some of Bonds’s statistics for three periods: career, 1987-1999, and 2003. The variables I use are On-Base-Percentage (OBP), OBP calculated with intentional walks excluded, non-intentional Walks per plate appearance, and Isolated Power (SLG-BA). The first three variables are good proxies for Bonds’s plate discipline. The less willing he is to swing at pitches outside the strike zone, the more likely it is he will see pitches he can hit from pitchers. The fourth variable captures his hitting power only. Steroids can influence his power, but it should have no effect on his plate discipline. While hitting discipline can increase his power.
OBP OBP-IBB BB/PA Iso-Power Career 0.431 0.407 0.144 0.310 1987-99 0.413 0.392 0.132 0.280 2000-03 0.517 0.477 0.185 0.439 StDev. 0.067 0.055 0.035 0.091
Clearly, Bonds is not just hitting the ball harder, he is improved his ability to wait for the right pitch. And interestingly enough, Bonds’s improved power is consistant with his growth in OBP. Using an OLS regression, I estimated the effect of OBP on Iso-Power for all teams from 2000-2003. I found that every OBP point is worth about .86 Iso-Power points; hence, .86*(.517) = .445. That is pretty darn close to his actual Iso-Power average.
This leads me to conclude one of the following must be true.
1) Steroids increases hitting discipline as well as muscle mass.
2) Bonds’s success is likely a product of becoming a better hitter, not using steroids.
My money is on the second. Thanks to Baseball-Reference for the stats.
Update: I’m bending a bit on this. See my post above.