testogram

A testogram is a graphical representation used in psychometrics to illustrate the relationship between observed scores and underlying latent traits. It is particularly associated with the work of Louis L. Thurstone and his development of multiple-factor analysis. A testogram visually displays the factor loadings of individual test items onto extracted factors. These loadings, typically represented by coefficients, indicate the strength of the association between an item and a particular factor. Items that have high loadings on the same factor are considered to measure that underlying trait. Conversely, items with low loadings on all factors or high loadings on multiple factors might suggest issues with item clarity or the distinctness of the extracted factors.

The construction of a testogram involves first performing a factor analysis on the intercorrelations of a set of test items. This analysis yields a factor matrix, which is then often subjected to rotation to achieve a simpler and more interpretable structure. The testogram is then created by plotting the factor loadings. Typically, two factors are plotted on orthogonal axes, with each item represented as a point or vector. The position of the point indicates its loading on each factor. Interpreting a testogram involves examining the clustering of items and their proximity to the axes, aiding in the identification of the latent constructs being measured by the test. While historically significant, modern psychometric software often presents factor structures in tabular form, though the underlying principles visualized by the testogram remain central to factor analysis.