PhD ceremony Ms. I.A.M. Smits: A methodological perspective on the analysis of clinical and personality questionnaires

PhD ceremony: Ms. I.A.M. Smits

Dissertation: A methodological perspective on the analysis of clinical and personality questionnaires

Promotor(s): prof. R.R. Meijer

Faculty: Behavioural and Social Sciences

Psychologists regularly use clinical and personality (C&P) questionnaires for the assessment of particular personality traits and / or psychopathological symptoms. To assess the quality of C&P questionnaires, specific measurement models are of interest. This thesis discusses the characteristics and usefulness of these measurement models for the analysis of C&P questionnaires.

Mokken scale analysis (Mokken, 1971) can be used to identify items that together form a Mokken scale. These Mokken scales are regularly interpreted as reflecting unidimensional scales, i.e., scales that measure a single trait. In this thesis, it is shown that this interpretation is not necessarily correct, because one Mokken scale can measure multiple traits and multiple Mokken scales can measure a single trait.

For the skew-normal factor model and the quadratic factor model, it was not clear which model is useful in which conditions. In this thesis, it is illustrated that observed data that follow any skew-normal factor model can be so well approximated with a quadratic factor model that the models are indistinguishable in practice. The reverse does not necessarily hold. Consequently, for the analysis across populations, the skew-normal factor model is preferred over the quadratic factor model.

This thesis also gives some examples of applications of measurement models for C&P questionnaires. Discussed are the use of the bifactor model for the evaluation of the specific contribution of subscale scores above the total scale score of the SCL-90 and measurement invariance tests (i.e., whether a questionnaire measures equally across populations) for the SDQ and Big Five personality factors.