Factor structure of the Hospital Anxiety and Depression (HAD) scale

S. Friedman and C. Even

Clinique des Maladies Mentales et de l'Encéphale (CMME), Centre Hospitalier Sainte-Anne, I rue Cabanis, 75674 Paris Cedex 14, France

J.-C. Samuelian

CMU de la Timane, Aix Marseille II, France

J. D. Guelfi

CMME, Centre Hospitalier Sainte-Anne, Paris, France

We would like to draw attention to the assertion by Mykletun et al (2001) that a two-factor structure best fits the Hospital Anxiety and Depression (HAD) scale, especially in individuals with mental problems. They stated that psychometric studies of this scale only involved small samples of non-psychiatric patients. However, we recently published the only factor analysis of the HAD scale based on a large population: 2669 ‘HAD completers’ from 3002 patients (89%) with major depression, DSM-IV criteria (Friedman et al, 2001).

Contrary to Mykletun et al, we found a three-factor solution using principal-components analysis with factors defined by eigenvalues >=1. One of Mykletun et al's reasons for rejecting the three-factor solution was that their third factor comprised heterogeneous items loading for both anxiety (items 7 and 11) and depression (item 14). Our three-factor structure discriminates the original depression factor and two separate constructs of anxiety: ‘psychic anxiety’ (items 3, 5, 9 and 13) and ‘psychomotor agitation’ (items 1, 7 and 11). This factor solution captured 48.6% of the variance and was relatively robust; it was not influenced by gender ratio and was also found in two random halves.

Two reasons may account for these discrepancies between our results. First, because of the high proportion of HAD scale non-completers (44%), Mykletun et al's sample may have been biased. Patients with depression are probably not prone to answer such surveys and may therefore be underrepresented. Second, the factor structure of the HAD scale may not be stable across different categories of subjects: those with heterogeneous mental problems and those specifically suffering from major depression.

The HAD scale is not only useful for its initial screening purpose. It also showed potential ability in assessing change in specific symptoms of anxiety (‘psychic anxiety’ and ‘psychomotor agitation’ factors of the scale) during antidepressant treatment (Friedman et al, 2001). Moreover, recognition and monitoring of psychomotor agitation has several clinical implications: it is a potential side-effect of some antidepressants (Nutt, 1999), it may predict antidepressant response (Flament et al, 1999), it may predict adverse outcome and increase the risk of suicide (Schatzberg & DeBattista, 1999).

EDITED BY KHALIDA ISMAIL

Declaration of interest

S.F. has formerly been CNS medical adviser for Pfizer France; J-C.S. has received fees from Pfizer France; J.D.G. has received fees from several pharmaceutical companies.

REFERENCES

Flament, M. F., Lane, R. M., Zhu, R., et al (1999) Predictors of an acute antidepressant response to fluoxetine and sertraline. International Clinical Psychopharmacology, 14, 259-275.[Medline]

Friedman, S., Samuelian, J. C., Lancrenon, S., et al (2001) Three-dimensional structure of the Hospital Anxiety and Depression Scale in a large French primary care population suffering from major depression. Psychiatry Research, 104, 247-257.[CrossRef][Medline]

Mykletun, A., Stordal, E. & Dahl, A. A. (2001) Hospital Anxiety and Depression (HAD) scale: factor structure, item analyses and internal consistency in a large population. British Journal of Psychiatry, 179, 540-544.[Abstract/Free Full Text]

Nutt, D. J. (1999) Care of depressed patients with anxiety symptoms. Journal of Clinical Psychiatry, 60 (suppl. 17), S23-S27.

Schatzberg, A. F. & DeBattista, C. (1999) Phenomenology and treatment of agitation. Journal of Clinical Psychiatry, 60 (suppl. 15), S17-S20.


 

Authors' reply

A. A. Dahl, A. Mykletun and E. Stordal

Department of Psychiatry, Aker University Hospital, N-0320 Oslo, Norway

EDITED BY KHALIDA ISMAIL

Friedman et al raise doubts as to the two-factor structure of the HAD scale reported by us. The size of our sample (n=51 930) allowed us to test our finding in several sub-samples. Using principal-components analysis, the same two-factor solution was also found in all sub-samples reporting somatic and psychiatric problems, as well as in all age- and gender-groups from 20 to 89 years. This indicates that the two-factor structure of the HAD scale is robust and stable. Therefore, eventual minor biases due to response rates cannot account for the discrepancy between Friedman et al's and our findings. Our third factor, which emerged only in sub-samples with low depression scores, always showed a low eigenvalue. Our results are in accordance with the conclusions of a recent literature review on the HAD scale (Bjelland et al, 2002) which concludes that a two-factor solution is most commonly found.

Friedman et al (2001) have a sample (n=2669) characterised by major depression (DSM-IV), which corresponds to high depression and probably variable anxiety scores on the HAD scale. When performing factor analysis, composition of the sample is essential for the results. If an inclusion criterion restricts the variance and covariance of the variables entered in the factor analysis, this will influence the factor solution found. The results by Friedman et al can be interpreted as a consequence of their restriction of their sample to major depression only, as this restricts the covariance between items on the HAD scale. In our sub-sample with various mental problems (n=2098) the two-factor solution is robust with high explained variance (82.1%).

Friedman et al's findings are of interest, however, since they answer the question: What is the factor structure of the HAD scale when anxiety appears in major depression? Comparing the fit coefficients between two- and three-factor solutions using confirmatory factor analysis must show the advantage of a three-factor solution. Friedman et al seem to presume that the factor structure of anxiety found in major depression is identical to that found for anxiety in the general population.

The advantage of population samples is that selection bias is minimised. In several of our studies based on the unselected HUNT-II population (from the Nord-Trøndelag Health Study) we have found results at variance with those of clinical samples (Engum et al, 2002; Wenzel et al, 2002). This could also explain the discrepancy between Friedman et al's and our results.

REFERENCES

Bjelland, I., Dahl, A. A., Haug, T. T., et al (2002) The validity of the Hospital Anxiety and Depression Scale. An updated literature review. Journal of Psychosomatic Research, 52, 69-77.[CrossRef][Medline]

Engum, A., Bjøro, T., Dahl, A. A., et al (2002) An association between depression, anxiety and thyroid function — a clinical fact or an artefact? Acta Psychiatrica Scandinavica, in press.

Friedman, S., Samuelian, J.-C., Lancrenon, S., et al (2001) Three-dimensional structure of the Hospital Anxiety and Depression Scale in a large French primary care population suffering from major depression. Psychiatry Research, 104, 247-257.[CrossRef][Medline]

Wenzel, H. G., Haug, T. T., Mykletun, A., et al (2002) A population study of anxiety and depression among persons who report whiplash traumas. Journal of Psychosomatic Research, in press.