Keywords: public mental healthcare, questionnaires, defects, implications

“Assessment, measurement and evaluation within public mental health; methodological and psychometric challenges”

The public mental healthcare system makes frequent use of questionnaires as part of other treatments, interventions and policies. This dissertation demonstrates that many questionnaires are sensitive to 'hidden defects', such as the effect of social desirability of questionnaires used in youth healthcare. While these defects are not discernible to the respondents, they may result in the incorrect use of questionnaires and thus form an important obstacle to valid assessment and decision making processes in public mental healthcare. By researching the working population and youth healthcare, this dissertation reveals that the impact of such defects can be considerable and that there are several methods to reduce it. The implication of this dissertation is therefore twofold. It reveals that increasing awareness of hidden defects in the use of questionnaires by both researchers and professionals is crucial, and also that any shortcomings in the questionnaire itself can be corrected.