The Common Factor Model

In Chapter 6, a psychometric conception of a homogeneous set of items was introduced, based on the classical Spearman single-factor model. In this conception, the items form a homogeneous set if they measure just one attribute in common—just one common factor. We can also describe such a set of items as unidimensional, because they indicate variation of respondents on a single dimension. Factor analysis is an important analytic tool for test validity, as well as for other possible applications. This chapter gives a more general account of the common factor model.