Is the difficulty index to be used when analyzing psychological tests?

Abstract

The present article is aimed to examine the applicability of the difficulty index within the framework of psychometric analysis of psychological tests. It is demonstrated that this index is often disregarded in traditional psychometric research due to its absence in the paradigm of confirmatory factor analysis, which is commonly employed by most psychologists. Analytical and empirical examples are provided to illustrate that difficulty is analogous to entropy, a measure of information quantity, and does not possess a unit of measurement. A comparison of both indices is conducted to assess their respective advantages and disadvantages. Recommendations are provided regarding their utilization in studies on the quality of diagnostic methods.