Psychometric work on the widely used Depression Anxiety and Stress Scales (DASS) has mostly used classical psychometrics and ignored common internet-administered versions. Therefore, the present study used not only classical, but also modern psychometrics based on item response theory (IRT) to evaluate an internet-administered version of the DASS (Dutch translation). Internet-administered DASS data were collected as part of a large internet-based study in the Dutch adult population (n = 7972). Initially, external correlates (i.e. demographics other measures) and some classical psychometrics (internal consistency, convergent/divergent validity) of the DASS scales were evaluated. Next, IRT was used to investigate the scales' dimensionality, discrimination and item-functioning. Finally, the DASS depression scale was further investigated by linking it to the more clinically-oriented Quick Inventory of Depressive Symptomatology (QIDS) using item response theory (IRT). Initial classical psychometric analyses supported the scales' internal consistency (alpha = 0.94-0.98) and convergent/divergent validity. IRT analyses showed that each of the DASS scales was only suitable to measure variations in a very narrow and rather mild severity range. Linking the DASS depression scale with the QIDS also showed that the DASS depression scale discriminated best in the mild-moderate severity range, but not at higher severity levels that were covered by the QIDS. In conclusion, the scales of the internet-administered DASS show good internal consistency and validity. However, users should be aware that the scales discriminate best at mild-moderate severity ranges in the general population.
Keywords: DASS; Internet-based; Item response theory; Linking; Psychometric; Validation.