Why do we trust exam results?

Poor results can wreck people's lives, but the thinking behind exams is crude and simply out of date

When I was in high school I took the ACT, a college aptitude exam used as an admissions criterion by most American universities. My score was in the lowest third of all students. That was painful enough but, adding insult to injury, the ACT score report informed me that, based on my score, my expected probability of succeeding at my hometown college, the University of Utah, was around 15%. As I remember it, my chance of success at my dream school of Harvard University was less than 3%.

I felt pretty hopeless about my future. After all, these stark percentages were endowed with the sober authority of mathematics. Before I took the exam, I had thought that one day I might become a scientist or neurologist, but no - what a silly fantasy that was.