When Blogging Leads to Blogging

March 19, 2009
Posted by Jay Livingston

As Mike’s comment yesterday suggested, I wasn’t the only one to blog the basketball paper (aka “Avis goes to the NCAA”). I certainly wasn’t the most methodologically sophisticated. Andrew Gelman and some of the Freakonomics commenters were.

Now Justin Wolfers has printed a rebuttal of sorts to these criticisms. It’s by the authors of the original paper, Jonah Berger and Devin Pope, who present a new graph showing the home team’s winning percentage for all halftime differences from behind by ten points to ahead by ten points.

They plot a curve to show the “expected” percentage for each point-differential.
(In the months following the 9/11 attacks, there was much hand-wringing about failure to “connect the dots.” So I have added a red line that does just that, making it easier to see the discontinuities, those points where the line turns down instead of continuing up.)

(Click on the chart for a larger view.)
Focus on the winning percentage when either the away team was losing by a point, or the home team was losing by a point. In both of these situations, the losing team did better than expected.
True, they did better than expected. But given the overlap in the standard-error ranges, the data still don’t provide a clear answer as to whether it’s better for the home team to be down by one or up by one at the half.* More curious, Berger and Pope say nothing about halftime ties, which turn out favorably for the home team more often than either minus one or plus one scores.

* Berger and Pope say that this is the wrong question: “Directly comparing the winning percentage of teams down by one with teams up by one is problematic.” That’s odd. It would seem that winning is the central question. The title of their paper puts it pretty clearly: “When Losing Leads to Winning.”

I guess that when the paper is finally published, they’ll change the title to “When Losing Leads to Doing Better than Expected.” Or better yet, “If You Can Make Halftime Prop Bets and the Score Is Tied and the Money Line is Close to Even, Sock It In on the Home Team.”

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