Everyone Should Learn Statistics

I spent the last two days on jury duty in the District of Columbia. (Whatever the broader shortcomings of D.C. municipal government, their process for hauling you into the jury pool every two years works with uncanny efficiency; watch this space for jury-related blog posts in early May 2014.) It was a DUI case, and, sidebar, before we talk about the need for statistics education, let me say this: If it at some point in your life you decide to spend a long Tuesday evening partying at the home of a friend / business associate known only as “Cesar,” and after the conclusion of said partying you elect to get home by driving 60 miles per hour through Rock Creek Park at 3:00 AM, and you get pulled over for speeding, and you fail the various standardized roadside sobriety tests, and get arrested for DUI, and rather than take a plea deal decide to avail yourself of your constitutional right to a trial by a jury of your peers, and when the time comes for you to testify under oath your attorney--your attorney--says to you, “Can you tell the jury how many beers you consumed that night, while you were partying with Cesar,” it may not be in your best interests to answer, “Nine, if you count the two I had after midnight, before getting in my pickup truck.” Just saying.

So earlier in the trial the arresting officer testified about the aforementioned standardized field sobriety tests, or “SFST’s.” Under cross-examination by the defense attorney, he testified that people who fail the first of the three standardized tests, the “Horizontal Gaze Nystagmus,” where they make you track a pen moving back and forth in front of your face, are 77 percent likely to have a blood-alcohol level over the legal limit of .08, and that when the test results are combined with the two other SFST’s, the percentage goes up to 83 percent. (According to the National Highway Traffic Safety Administration, the first test actually “allows proper classification of approximately 88 percent of suspects” and gets up to 91 to 94 percent in combination with the others, so the officer was understating his case.)

During closing arguments, the defense attorney focused on those numbers. 77 percent, he said, was like “C-plus” on a test in school. Not an “A,” not even a “B,” but a “C,” and if we’re going to expect our children to do better than that, then by God shouldn’t we expect the same from our police?! It was kind of like this, without the funny.

The problem of course is that the percentage of questions you get right on an algebra quiz and the statistical likelihood of one thing being correlated to another thing are two very different things. The defense attorney either didn’t know that, or assumed the jury didn’t know that, but either way it points to a terrible statistical illiteracy in the general populace. Which is not surprising, given that statistics isn’t part of the standard curriculum schools require students to complete in order to get a high-school or college diploma. Math education is still largely interpreted as a progression through algebra and geometry to calculus. And I’m not against working harder to improve math education. But in terms of things you really need in order to make your way in modern society, statistics is way, way up there, above a lot of things that are currently lodged in the curriculum. Fitness for jury service is one of the few tangible requirements of citizenship--New York relied on it in part when evaluating the adequacy of the state’s funding programs. Everyone should learn statistics. Otherwise slightly wiser (or less honest) drunk drivers will be able to menace the highways with impunity.