the happy conservative

I apologize for being out of the loop; I’ve been doing LSAT practice tests.

I’ve heard people, otherwise rational people, complain that the LSAT measures only one’s ability to take tests, and not one’s probability of success at law school.

I heard the same argument about the ACT when I applied to college four years ago, and about state standardized exams and the No Child Left Behind Act, despised by conservatives and liberals alike. And teachers. And students. And janitors. And administrators.

I’ve written elsewhere about using the ACT as a substitute for state-sponsored standardized tests.

The reasoning behind that prescription lies buried within an essential understanding of the incentive structure of college admissions. Why do colleges use standardized exams? Colleges are ranked on the basis of the exam scores that they admit. But this is only part of the incentive. Included as well are the graduating students’ placements, which are determined simultaneously by their talents as students and the perceived quality of the institution.

A college (or law school) wants to place its students as well as possible. It therefore needs a method of determining the quality of those students, and their probability of success, prior to admittance. GPA is useful, but not terribly. GPA depends on a number of factors that are difficult to observe: student quality, teacher quality, course difficulty, relative grade inflation. Unless you can sift the confounding factors, GPA as a tool for determining student quality is limited at best.

Standardized exams do not remove all of the simultaneity. Exam scores are jointly determined as well, by student quality, level of preparation, memory, and breakfast. But then again, as an educational institution, you don’t really care if the factors are confounded. People who eat breakfast and get up early are going to do better at class, too, on average. And they’re going to place better. People who take the time to prepare will also place better.

There is no way to measure a given student’s probability of success in school. The best a college can hope for is to find a suitable instrument, something that maps onto success in school fairly well. For profit maximizing colleges, the choice is “test-taking ability.”