Of course, lots of people have always thought Mr Levitt was in the wrong. Even if abortion cuts crime, it is still immoral, they fulminate. But this is largely beside the point: Mr Levitt's research does not take a position on abortion's social virtues, but aims merely to uncover its societal effects. Besides, for someone of Mr Levitt's iconoclasm and ingenuity, technical ineptitude is a much graver charge than moral turpitude. To be politically incorrect is one thing; to be simply incorrect quite another.
But what is most amazing is that despite all the statistical significance being eliminated from their panel data set being eliminated when the results are done Donohue and Levitt's way with the the data they want to use, John Donohue now says what they wanted to do:It may be asking too much of the numbers to convince everybody. “The debate over abortion and crime will not be resolved within the parameters of our paper,” says Mr Donohue. He thinks the arrest figures are “muddy” and the state population data “sloppy”. Combining the two generates so much noise, it is hard for the statistical tests to hear anything. Ted Joyce, a professor at Baruch College (part of the City University of New York), who has had his own methodological disagreements with Messrs Donohue and Levitt, also thinks the debate is stretching the data too far. He points out that if you add controls for 50 states and 12 years—as Messrs Foote and Goetz do, and as Messrs Donohue and Levitt meant to do—you are, in effect, holding another 600 things constant. This robs the data of most of their variety, and of much of their ability to explain anything.
There was no warning that these were the wrong tests at all in either of their previous papers or in Levitt's book. Levitt now refers to the “collage of evidence," but the panel data was the only test that really amounted to anything worthwhile. The rest of the data was merely cross sectional or time series.
Labels: Abortion, Crime, JohnDonohue, SteveLevitt