Assessing psychological distress in patients with skin diseases: reliability, validity and factor structure of the GHQ-12

Objective We studied reliability validity and factor structure of the 12-item General Health Questionnaire (GHQ-12) in dermatological patients. Methods Subjects attending a dermatological outpatient clinic were administered the GHQ-12 and the Skindex-29. A random subsample was mailed another copy of the questionnaires to be completed within 1 week. Results A total of 2579 subjects completed the GHQ-12. The internal consistency of the GHQ-12 was high (Cronbach's alpha = 0.88). Test-retest reliability on 137 subjects was also fairly satisfactory (intraclass correlation coefficient = 0.72), notwithstanding a re-test artefact probably related to reassurance from the physician. Evidence of construct validity was provided by the pattern of correlation between scores on the GHQ-12 and on the scales of Skindex-29, which were as hypothesized. Also, GHQ-12 scores of patients in different clinical groups varied as hypothesized, with patients affected by inflammatory skin diseases scoring significantly higher than patients with isolated skin lesions. We obtained both a two-factor and a three-factor solution: the latter seemed theoretically more appropriate, although the first may have practical advantages. A 'social dysfunction' factor emerged in both analyses, while the other items loaded on a 'general dysphoria' factor or on two separate factors interpreted as 'anxiety' and 'loss of self-esteem'. Conclusions The GHQ-12 is a reliable and valid instrument with a factor structure that is quite stable across different samples as well as across diverse cultures. Its brevity and easiness of completion make it a useful tool to assess psychological distress in dermatological patients.