Interleague Attendance: a Less Deceptive Look

As the weekend draws to a close, so to does our first taste of interleague play in the 2009 season. One of the hottest topics this side of steroids in the modern game, interleague play has strong proponents on both sides of the issue. One of, if not the, central claims of supporters is the large attendance spike reported by MLB for interleague games. In 2007, MLB claimed attendance rose over 13% historically in interleague games and over 15% in 2007. The fans want to see it, teams bring in more revenue, what's not to like?

For starters, there's MLB's deceptive attendance reporting. There are a number of issues here, so first let's start with the 2007 exclusive figures. MLB tries to make it appear that interest in interleague games is actually higher in 2007 than it has been historically. One of the points of opposition to interleague play is that it has grown stale, and the initial excitement fans showed has waned over the years. MLB is indicating here that that is not the case. The problem with that is, the season was not over when they released these figures, and so the half-season figure from 2007 was not comparable to the historical number they were comparing it too. Most of those interleague games were from June, whereas the non-interleague games were more heavily weighted with April and May games, where attendance is always significantly lower. Once the non-interleague sample picked up more summer games, the non-interleague game attendance also rose. By the season's end, that 15.4% rise in attendance in interleague games was halved to a 7.6% increase, clearly much lower than their historical rise. Other recent years all show smaller increases than the early years of interleague play. However, MLB still has their skewed midseason figures posted almost 2 years later with no mention that the figure they reported for the year at the time is not even close to accurate for the year as a whole.

That is just one of many issues with MLB's reports, however. The historical attendance figures reported by MLB are also rife with further deception. For one, most (2 out of every 3) interleague games are played on weekends (Friday through Sunday), while most non-interleague games are played on weekdays. Attendance just happens to be about 19% higher on weekends than on weekdays. The figures MLB reports assume that the only factor that affects attendance is whether the game is interleague or not. This clearly isn't the case. A game's attendance is affected by a number of other factors, including:

-where the game is being played (a game in Yankee Stadium will have a higher attendance than one at PNC Park no matter who is playing)
-the day of the week
-the month
-whether the game is a day or night game

Of course, you could ignore these other factors if they could be expected to even out over a long enough period of time, which is generally what we do with stats when we want to measure one thing. The problem here is that none of these other factors do even out over time. MLB deliberately schedules interleague games when attendance is already likely to be higher.

For another example of the above issues not evening out, consider that because of the different number of teams in each league, AL teams have more interleague games in their parks, and NL Central teams have fewer than even other NL teams. So while the Yankees had hosted 106 interleague games through 2008, the Pirates had only hosted 86.

Something is very clearly wrong with the simplistic figures MLB gives us. None of the factors listed above that all influence attendance are accounted for in their attempt to isolate the effect of interleague play on attendance. Since MLB is not interested in giving us an accurate assessment of the effect of interleague play on attendance, we'll have to take our own look. For that, we turn, as always, to Retrosheet, where we can use gamelogs to isolate the effect of interleague play on attendance. To do this, we look at games that happened in the same park, in the same month, on the same day of the week, and either at day or night, and we compare the attendance only based on whether the game was interleague or not. So an interleague game played on a Friday night in Busch Stadium III in June is compared only to non-interleague games that also happened on a Friday night in Busch Stadium III in June. And so on for every interleague game from 1997 to 2008.

We find that attendance did rise, but only 5.9%, much less than MLB reports. We also find that the spike was higher in the early years of interleague play: in the last 5 years, attendance rose only 3.6%. So attendance does rise a bit in interleague games. Just not nearly as much as MLB tells us it does. We also can't say for certain, as we are often told, that this is a sign of greater fan interest.

Often times, the increase in attendance comes from fans of the road team that travel to support the team on the road. For example, Cardinal fans travel in hordes across the state to Kauffman and often return with stories of more red in the stadium than blue. Cub fans can easily follow their team to the new Comiskey. Does this mean they are more interested in the Cardinals playing the Royals than the Dodgers or the Cubs playing the Sox than the Mets? Not necessarily. There are plenty of reasons a Cardinal fan would go to Kansas City and not L.A. for a game, or a Cub fan would go to Comiskey but not Citi Field that have nothing to do with his or her level of interest in each game, namely that it's just easier and more realistic to get there. We can say for certain that interleague's attendance increases bring more revenue to teams (which is the other part of the argument). We can't really gauge fan interest, however, especially from such a modest spike.

Once we get past MLB's skewed presentation of the results, we can see that the majority of the increase in attendance in interleague games has absolutely nothing to do with them being interleague. What has essentially happened is that Bud Selig has observed that attendance naturally increases on certain dates throughout the year and always has, and he has somehow found a way to take credit for that. Or at least that's the way he's presenting it by so deceptively inflating the impact of his brainchild.