Inter-Division Play: AL Dominance Explained?

In my last post, I examined how pitchers who can hit has an advantage over pitchers who don't, then thought about the advantage for the AL team in terms of the DH during that series. That also might explain the AL's dominance in inter-division play. If NL pitchers aren't that good in the first place, then the AL pitchers' lack of hitting practice doesn't matter much in terms of advantage for the NL over the AL when playing in NL. However, when you are in an AL city, you often have 1B-type hitters (high 800 OPS) in the DH position for the AL team but a replacement level hitter (probably high 600's OPS) in the DH position for the NL team.

Since that is roughly the difference for my examination using the Giants data and Vizquel's OPS (.467 OPS for the #9 hitter vs. .671 OPS for Vizquel), that means that the AL gets roughly one extra win for every 32 games played in the AL. That means for every 162 games played in AL cities, between two otherwise equal teams, the AL would only be 81-81, but with their DH advantage, they would be 86-76.

How does this look in practice:

• Last season, they won 137 games out of 252, for a winning percentage of .544, which works out to a 88 win season. Based on my assumptions above - equal at NL, unequal at AL - the AL teams should win around 130 games, so it appears that the AL is better than the NL by a slight margin.


• In 2006, they won 154 out of 252 for a much larger margin.


• In 2005, 136 wins out of 252.


• In 2004, 127 wins vs. 125 losses, so they were actually below average there.


• In 2003, 115 wins vs. 137 losses, so the NL were clearly better this year.


• In 2002, 123 wins vs. 129 losses, again NL better.


• In 2001, 132 wins vs. 120 losses, AL back ahead again


• In 2000, 136 wins


• In total, for the 2000's, the AL were 1060-956 for a .526 winning percentage or 85 wins in a 162 game season

My theoretical model predicted a 84 wins season. That is roughly the rate (85 wins) that the AL has won at in the 2000's, suggesting that the wide ups and downs in each season is roughly random fluctuations around the mean. Based on this, the AL and NL have basically been equal all these years, with a slight advantage to the AL, but because of the imbalance at the DH position all these years, they have appeared to be much more dominant.