Paul E. Newton provides an insightful and scholarly overview of central issues in validity theory. As he notes, many of the conceptual problems in validity theory derive from the fact that the word "validity" has two meanings. First, it indicates "whether a test measures what it purports to measure." This is a factual claim about the psychometric…

In his opening statements, Humphry takes a critical attitude with respect to psychometric modeling. As he advances and discusses Michell's well-known criticisms, the reader is certain that this paper must have something on offer that deviates considerably from conventional psychometrics. After all "most psychometricians have either explicitly or…

Test equating under the NEAT design is, at best, a necessary evil. At bottom, the procedure aims to reach a conclusion on what a tested person would have done, if he or she were administered a set of items that were in fact never administered. It is not possible to infer such a conclusion from the data, because one simply has not made the required…

This paper formulates a metatheoretical framework for latent variable modeling. It does so by spelling out the difference between observed and latent variables. This difference is argued to be purely epistemic in nature: We treat a variable as "observed" when the inference from data structure to variable structure can be made with certainty and as…

Achilles and the tortoise want to predict peoples' running performance from their age. In determining age the tortoise has cleverly asked his participants for their passports and has noted their date of birth, before letting them run half the distance between Achilles and himself. Achilles, however, has given his participants a questionnaire…

Nesselroade, Gerstorf, Hardy, and Ram (this issue) propose to "filter out" idiosyncrasies of dynamic processes at the level of the individual through the application of dynamic factor analysis. The problem that they deal with is that individuals may differ in the items that are "salient" for a given construct, so that the same measurement model…