A DECADE ago when I was an undergraduate psychologist, a departmental librarian called Anne was doing something any psychologist would say was impossible. Every year, with near-perfect accuracy, she would predict which third-year undergraduates would be awarded first-class degrees. Anne didn't know how their essays were rated, what A-level grades they had under their belts, or how they scored on IQ tests. (All information many would say was essential to forecasting final results.) All she knew was how often she had seen students in the department library: reading course notes, photocopying journals, borrowing books. And the handful of students who...