Details

The Demonstration uses the prevailing American calibration of grades, which requires them to lie between 0 (an "F") and 4 (an "A").

The Demonstration assumes, incorrectly, that GPAs are normally distributed. In fact, this is unlikely to be the case. GPAs are calculated as the mean of draws from an underlying censored distribution. The underlying distribution is censored because, generally speaking, grades cannot exceed a maximum value (such as 4.0) or go below a minimum value (such as 0). The mean of these draws must, therefore, itself be censored to lie between the minimum and maximum values. Still, some experimentation suggests that the assumption that GPAs are normally distributed does not generally result in large errors.

The idea for this Demonstration is suggested in Ian Ayres, Super Crunchers, New York: Bantam Dell, 2007.