From the editorial: The article continues the author\rq s History of mathematics series. In this article he considers factor analysis applied to test scores. The underlying idea in factor analysis is to determine if a number of observables $y_1,y_2,\dots ,y_n$ can be linearly related to a smaller number of unobservable factors $f_l,f_2,\dots ,f_k$. For example the observables might be scores from many different students in $n$ different tests.