Methodological artifacts in dimensionality assessment of the Hospital Anxiety and Depression Scale (HADS)

Objective
The Hospital Anxiety and Depression Scale (HADS) is a brief, self-administered questionnaire for the assessment of anxiety and depression in hospital patients. A recent review [7] discussed the disagreement among different studies with respect to the dimensionality of the HADS, leading Coyne and Van Sonderen [8] to conclude from this disagreement that the HADS must be abandoned. Our study argues that the disagreement is mainly due to a methodological artifact, and that the HADS needs revision rather than abandonment.
Method
We used Mokken scale analysis (MSA) to investigate the dimensionality of the HADS items in a representative sample from the Dutch non-clinical population (N = 3643) and compared the dimensionality structure with the results that Emons, Sijtsma, and Pedersen [11] obtained in a Dutch cardiac-patient sample.
Results
We demonstrated how MSA can retrieve either one scale, two subscales, or three subscales, and that the result not only depends on the data structure but also on choices that the researcher makes. Two 5-item HADS scales for anxiety and depression seemed adequate. Four HADS items constituted a weak scale and contributed little to reliable measurement.
Conclusions
We argued that several psychometric methods show only one level of a hierarchical dimensionality structure and that users of psychometric methods are often unaware of this phenomenon and miss information about other levels. In addition, we argued that a theory about the attribute may guide the researcher but that well-tested theories are often absent.
Keywords: Anxiety, Depression, Dimensionality, HADS, Mokken scale analysis