ABSTRACT
Connection With Other Chapters
Chapter 2 reviewed the most influential theories of measurement, and chapter 3 discussed psychometric models that are often used in analyzing test scores. Theories of measurement are of central importance to test score interpretations in terms of measurement. Psycho-metric models are of central importance to the statistical analysis of test scores. Both measurement interpretations and statistical analyses of test scores figure prominently in validation research. Hence it is important to analyze how measurement theory and psychometric models are connected. This chapter analyzes the relation between psychometric models and theories of measurement. In particular, it discusses the question of whether psychometric test scores can be justifiably interpreted as measurements.
The relation between measurement theories and psychometric models is highly relevant to validity. One commonly sees papers in which researchers claim that they have measured something, whereas the defense of this claim only involves psychometric modeling. For instance, one might claim that one has measured reading ability, and justify this claim through the supporting claim that a unidimensional Item Response Theory model fits the item scores. For such arguments to work, there must be a connection between the fit of the model and the status of test scores as putative measurements. Somehow the fit of the model must count as evidence for the measurement claim. That requires a link between psychometric models and theories of measurement.