Evaluating psychological distress data.

Kessler k psychological distress scores are analyzed using a count model and item response theory (IRT) models are applied to the items which produce the k score and generate an alternative distress score, θ . Other ways of utilizing the constituent items are also examined. The data used in the analysis comes from the 2014 National Survey of Drug Use and Health. Three important results emerge. First, θ and k are not highly correlated and their distributions are quite different. The k score gives a much more favourable picture of mental health than θ . Second, k does a much better job in explaining participation in treatment programs than θ suggesting a very limited role for IRT methods in the analysis of psychological distress data. As a diagnostic tool k is an effective and simple way of summarizing the item data. Third, for researchers interested in which individual characteristics determine psychological distress better results are obtained by analyzing the six constituent items which are used to generate the k score using ordered probability models rather than k itself.