Season Home Run record 1: Bonds, McGwire, Maris, Ruth, Craveth.

Click link to view lots of details on these eight modern record setting seasons.  The percent difference is between the player's home run (HR) rate per at bat (AB) and that of the league that season minus the player's HR and AB.  Babe Ruth out homered every other team in both 1920 and 1927, so his percent of the American League (AL) HR was substantial.  In his four record setting seasons:
12.08%
14.63%
12.37%
13.67%

(P-(L-P))/((L-P)
In this equation each letter represents (HR/AB) for either the player or the league minus the player.  The result is the number of times the player's HR rate is better than all the other batters in that league that season.  For instance in 1919 Babe Ruth was 10.76 better than the other AL batters.

Player Year  HR (HR/AB)
Gavvy Craveth 1915 24 8.23
Babe Ruth 1919 29 10.76
Babe Ruth 1920 54 14.54
Babe Ruth 1921 59 10.05
Babe Ruth 1927 60 11.19
Roger Maris 1961 61 2.81    expansion year
Mark McGwire 1998 70 3.86    expansion year; 1993 was also an expansion year
Barry Bonds 2001 73 3.67

Note that Maris has the least advantage over the other player's in his league that season.  I intend to do a detailed analysis of that 1961 record setting season.

I will follow with more comments on the rest of the data in subsequent posts.  See:

Home Run Proficiency relative to League. Thursday, December 13, 2012