Hospital Anxiety and Depression (HAD) scale: factor structure, item analyses and internal consistency in a large population

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-Trondelag 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 subscales 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 Declaration of interest The Norwegian Research Council and Novo Nordisk Pharmaceuticals (Norway) supported this study.