December 28, 2004

Interleague Play

An Attendance Study

by Jeff Hildebrand

Eight years into the concept, MLB stands by its creation of interleague play, usually with a variation on this theme: "Fans love interleague play. In 2004, interleague play raised attendance by about 10%." Now, on one level this is accurate; interleague games had an average attendance of 32,914, while the intraleague games averaged just 30,112, so the interleague average is 9.3% higher. However, as Joe Sheehan has frequently pointed out, the data driving this claim is flawed and stacked in favor of interleague play. The primary problem is the issue of when games are played during the year.

There are two major divisions that can be made in terms of the schedule, both of which can have significant impacts on the number of people who will show up to a game. The first is the time of year, the summer months versus spring and fall months. Games played in June, July, and August are more likely to draw good crowds than games in April, May or September are. The weather is far more likely to be conducive to doing something outdoors during the summer. In addition, during the summer kids are out of school, and therefore families are more likely to come out to a game, especially a night game. The second division is weekday games versus weekend games, with weekend games obviously being more likely to draw a larger crowd. Since most Friday games are evening games and Sunday games are afternoon games, we'll call games on Fridays, Saturdays, and Sundays weekend games.

Putting these two factors together, you get that weekend games during the summer are likely to be the best for attendance while non-summer weekday games will be the worst. Let's look at the distribution of interleague and regular games using these distinctions for a typical team's schedule.

                   Interleague     Regular
Summer weekend         67%           21%
Summer weekday         33%           25%
Non-summer weekend      0%           25%
Non-summer weekday      0%           29%

The interleague games are heavily skewed towards the optimal calendar slots and as a result, the other games are skewed the opposite direction.

If we accept the idea that the straight comparison is a bad idea, the next question is how to get a better comparison. We can do that by using a "paired" comparison, i.e. we match up interleague games with other games based on the divisions mentioned above. For most teams this means using the first three weekday games after June 7, this year's start of interleague play, and the first six weekend games after that date. Some teams played fewer interleague games and in those cases the number of regular games used was reduced in order to match the interleague schedule. In addition, the last interleague game, an August 30 makeup game between the Phillies and the White Sox, was dropped because there was no good equivalent game to match it with.

So if we used that paired comparison, does interleague play still increase attendance? Yes, but by nowhere near as much as its boosters would like to proclaim. This year's interleague games averaged 33,023 fans, while the matching regular games averaged 32,453, an increase of 1.8% for the interleague games. Indeed this would seem to indicate that more than 80% of the supposed benefit of interleague play is merely a reflection of when the games are played.

An obvious possibility is that last year was just a fluke year or maybe the regular games which happened to match up with the interleague games featured unusually high attendance. Thanks to Retrosheet, it's possible to repeat the process for previous years. As with the 2004 data, the first Monday in June is taken as the starting point for the summer months and the occasional oddly placed makeup game was ignored. The results for the past four seasons:

Year    Claimed gain    Matched-pair gain
2001       13.0%              4.8%
2002       15.1%              6.0%
2003       11.5%              1.0%
2004        9.3%              1.8%

Clearly last season was not a fluke, but a reflection of a very sharp difference between the claimed benefits of interleague play and the actual boost in attendance. Yes, there does seem to be some boost caused by interleague play, but it's nowhere near the double-digit percentage jump that its backers like to claim. 2002 was the year that the "rotating" interleague scheduling started, so each team played teams it hadn't faced before, which may account for the jump in that year.

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