Interleague Attendance Nonsense

[Sky: Great FanPost from Eric.  Bumped to the front page.]

I've often seen articles and blog entries online about how great interleague is for attendance.  And then some numbers get quoted that confirm that.  From 2000-2008, the average interleague game had an attendance of 33,284 and all other games 29,981.  That is +11%!  Wow, interleague play is a GREAT thing for the teams/owners.

Well, not quite true.  The distribution of games isn't the same.  66% of the interleague games in the sample were Friday through Sunday, compared to just 45% for the non-interleague games.  I ran the attendance figures by day of week and got the following:

Mon +3.3%
Tue +6.7%
Wed +6.0%
Thu +3.3%
Fri +7.2%
Sat +7.1%
Sun +9.2%

If they had the same distribution of days of week, I come up with an expected attendance of 31913 per game; this nearly cuts the edge in half!

But, then the distribution on the calendar is also not the same; 87% of the interleague games were in June or July, while it was about 17% per month for the others.

Using just June and July the weekend distribution was still similar, 64% vs 44%; here are the attendance numbers by day of week for just those two months:

Mon +2.0%
Tue -0.9%
Wed -3.2%
Thu -4.9%
Fri +0.6%
Sat +2.6%
Sun +6.3%

Again, if they had the same distribution of days of week, I come up with an expected attendance of 31719 per game; this puts the two groups almost exactly even [Interleague +0.4%].

I'm going to restate that- if the interleague games weren't lumped onto Friday, Saturday and Sunday, there would be practically no difference in attendance [about 1000 total extra tickets per team per year, maybe 100 per game].

As the next pass I'll try and identify particular series that may outperform the rest [Mets-Yankees, Cubs-White Sox, Dodgers-Angels, etc]

Sky's edit: There are some more excellent charts and analysis in the comments, so read on...