Abstract

Background The Hospital Anxiety and Depression (HAD) rating scale is a commonly used questionnaire. Former studies have given inconsistent results as to the psychometric properties of the HAD scale. Aims To examine the psychometric properties of the HAD scale in a large population. Method All inhabitants aged 20–89 years ( n =92 100) were invited to take part in The Nord-Tr⊘ndelag Health Study, Norway. A total of 65 648 subjects participated, and only completed HAD scale forms ( n =51 930) formed the basis for the psychometric examinations. Results Principal component analysis extracted two factors in the HAD scale that accounted for 57% of the variance. The anxiety and depression sub-scales shared 30% of the variance. Both sub-scales were found to be internally consistent, with values of Cronbach's coefficient (a) being 0.80 and 0.76, respectively. Conclusions Based on data from a large population, the basic psychometric properties of the HAD scale as a self-rating instrument should be considered as quite good in terms of factor structure, intercorrelation, homogeneity and internal consistency.