Thursday, July 3, 2008

Inter-League Baseball Results

In my 13 June post, I reminded my loyal Godivan readership that American League (AL) baseball teams have dominated inter-league play over the past few years. And, this year was no different. With one rain date to be made up later this season, AL teams have won 149 out of 251 games so far or 59%.

AL superiority is no secret. What I wanted to investigate was whether the odds offered generally foolish baseball bettors correctly reflect AL dominance. Suppose you were a player in a non-profit office pool with points based on posted odds. Our expectation is that gaming houses set odds to line up an even proportion of betting on each team so that the house profit comes from the 5% commission implicitly built into the odds. If the odds are calibrated correctly, we would expect an all-AL strategy picking inter-league winners (or any other baseball pool picking strategy) to generate net point losses of 5% over a long period of time.

In fact, with an all-AL strategy you would be +34.6 so far this year with one point awarded to an AL overdog winner, the odds awarded as points to an AL underdog winner (e.g., 1.25 for a +125 underdog), -1 deducted from an AL underdog loser and the odds deducted from an AL overdog loser (e.g., -1.25 for a -125 overdog). It’s interesting to note that this breaks down to +25.8 from AL teams’ 57% record when visiting National League (NL) opponents and +8.8 from the AL’s 62% record playing host. In other words, odds favouring AL teams hosting inter-league games turned out more accurate than odds set for AL teams on the road in NL parks.

So, we have preliminary evidence that the fools who bet on baseball may not be correctly valuing AL dominance. Of course, one season of 251 inter-league games is not a large enough sample to draw a firm conclusion. But, I will be interested to follow this trend in future years to see whether the pattern recurs.

Thanks largely to my simple approach of picking all AL teams in inter-league match-ups, I am ranked 6th at

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