Super Crunchers by Ian Ayres

assignments to test for impacts. However, it’s also possible for Super Crunchers to piggyback on randomized processes that were instituted for other purposes. There are in fact over 3,000 state statutes that already explicitly mandate random procedures. Instead of flipping coins to create data, we can sometimes look at the effects of randomized processes that were independently created. Because some colleges randomly assigned roommates, it became possible to test the impact roommates have on one another’s drinking. Because California randomizes the order that candidates appear on the ballot, it became possible to test the impact of having your name appear at the top (it turns out that appearing first helps a lot in primaries, not so much in general elections where people are more apt to vote the party line).
    But by far the most powerful use of pre-existing randomization concerns the random assignment of judges to criminal trials. For years it has been standard procedure in federal courts to randomly assign cases to the sitting trial judges in that jurisdiction. As with the alphabet lottery, random case assignment was instituted as a way of assuring fairness (and deterring corruption).
    In the hands of Joel Waldfogel, randomization in criminal trials has become a tool for answering one of the most central questions of criminal law—do longer sentences increase or decrease the chance that a prisoner will commit another crime?
    Waldfogel is an auburn-haired, slightly balding imp who has a reputation for being one of the funniest number crunchers around. And he has one of the quirkiest minds. Joel often shines his light on overlooked corners of our society. Waldfogel has looked at how game show contestants learned from one season to the next. And he has estimated “the deadweight loss” of Christmas—that’s when your aunt spends a lot on a sweater that you just can’t stand. He’s the kind of guy who goes out and ranks business schools based on their value added—how much different schools increase the expected salary of their respective students.
    To my mind, his most important number crunching has been to look at the sentencing proclivity of judges. Just as we’ve seen time and time before, random assignment means that each judge within a particular district should expect to see the same kind of cases. Judges in Kansas may see different cases than judges in D.C., but the random assignment of cases assures that judges within any particular district will see not only about the same proportion of civil and criminal cases, they will see about the same proportion of criminal cases where the defendant deserves a really long sentence.
    Waldfogel’s “a-ha” moment was simply that random judicial assignment would allow him to rank judges on their sentencing proclivity. If judges within a district were seeing the same kinds of cases, then intra-district disparities in criminal sentencing had to be attributable to differences in judicial temperament. Of course, it might be that certain judges by chance just received a bunch of rotten apple defendants who really deserved to go away for a long time. But statistics is really good at distinguishing between noise and an underlying tendency.
    Even though federal judges are required to follow sentencing guidelines—grids that foreordain narrow ranges of sentences for defendants who committed certain crimes—Waldfogel found substantial sentencing disparities between judges. There really are the modern-day equivalent of “hanging judges” and “bleeding hearts”—who found ways to manipulate the guidelines to increase or decrease the time served.
    These differences in sentencing are troubling if we want our country to provide “equal protection under the law.” But Waldfogel and others saw that these disparities at least have one advantage—they give us a powerful way to measure whether longer