The AL is better than the NL, right? On LGT, at the very least, the NL is often referred to as the weaker league and, according to the prevailing public opinion, it isn't really all that close.  

Recently, one of my close friends and I had a discussion about this and, with interleague play creeping up, I thought this could be relevant, or at least interesting to discuss here.  As the Indians, LGT-reading fan, I clearly believed that the AL was leaps and bounds ahead of the NL while he, as a huge Mets fan, naturally disagreed.  I wanted to look more deeply into this and I soon got my opportunity in my money and banking class that afternoon.  

In order to understand the issue, it is important to recognize which sets of data are useful.  I eliminated world series games because that is too small a sample size (it seems as though anything can happen in a 7 game series) and all-star games because they are an inexact science, at best.  Finally, I didn't feel comfortable relying on the statistics of players who transfer from one league to the other - there is so much that goes into a player's performance from one year to the next that it would be hard to attribute any difference in statistics to a disparity in the leagues.  The only thing I could think of to look at was the records of both leagues in interleague play since it began in 1997.  My friend hypothesized that, while the AL would have a higher win % than NL teams, it is because of they are constructed specifically around the DH, which gives them an unfair advantage in home interleague games.  The idea here is that the AL teams use a professional DH (though we can argue how much of an advantage that has gained us this year) while the NL teams usually uses its bench players as their DH.  He even went as far as to guess that the NL is better than the AL, and that it will be reflected in the interleague records at NL stadiums.  We, obviously, needed to look at interleague records at both AL stadiums and NL stadiums.  Here is what I emailed him during that class (stats all thanks to B-Ref):

First, I took the overall interleague records since interleague play started (1997).  As we expected, the AL is leading, but only slightly (51%).  Over the last 5 years it has shifted slightly in the AL's favor (53%).  So the AL has been better but not by much.  In games played @ AL stadiums, the AL has a 59% win pct. over the last 10 years and a 60% win pct. over the last 5.  In games played @ NL stadiums, as you hypothesized, the NL actually holds the advantage (54% over both time periods).  It seems as though you were right - the AL holds a significant advantage in games played with a DH and the NL, somewhat surprisingly, holds an advantage in games played in the NL.

Here's where it gets interesting, at least in my mind.  It occurred to me that maybe the NL wins more @ home because there is just a straight-up home field advantage.  I looked at the numbers from all the overall games that have been played in baseball over the last 5 & 10 years.  The home team, in both periods, wins about 54% of the time, or exactly the rate at which NL teams win interleague games at home.  Basically, what this means is that NL teams win @ home exactly as much as you would expect them to because they are playing at home.  The advantage AL teams have at home (at thus in interleague play overall) can be broken down into two components: their home field advantage and their DH advantage, though it is impossible to separate the two.

My ultimate conclusion is this - the NL and the AL, statistically speaking, are actually equal.  The NL wins @ home 54% of the time because home teams in general win 54% of the time.  The AL wins @ home 60% of the time because they are built to play @ AL stadiums whereas NL teams are not.

That is what I concluded upon this writing a few weeks ago.  I have since decided that my friend's supposed (or actual) unfair AL advantage can be flipped and be applied to the NL teams as well.  That is, NL teams are built for deeper benches, speed and defense, and their managers are more adept at employing the "small ball" strategies that only apply because the pitcher has a spot in the batting order.  This can be seen as a specific advantage to the NL and, thus, their winning percentage in home interleague games should in fact be higher than the 54% of the time that the home team wins in general.  Since it is not, I'll say that the NL is indeed worse than the AL (according to the most concrete data we can use), but the difference is substantially more minimal than we'd like to think.  

Apologies for the length of this post - I am really curious to know what other directions this sort of "research" can be taken.  I would love to hear some discussion about this - LGT!  By the way, with all this lack of attention in money & banking, I still pulled the A-!