Questionnaire techniques in assessing acne handicap: reliability and validity study.

The purpose of this study was to examine and compare the reliability and validity of two acne-specific measures, the Cardiff Acne Disability Index (CADI), the Acne Disability Index (ADI) and a general health status instrument, the United Kingdom Sickness Impact Profile (UKSIP). The test-retest reliability was carried out for the UKSIP, ADI and CADI with an interval of 10 days in 70 patients with acne. The correlation coefficient for the overall UKSIP score was high (r = 0.99, p < 0.001) for the CADI was 0.96 (p < 0.001) and for the ADI was 0.98 (p < 0.001). Individual category score correlations in the UKSIP and ADI were greater than 0.83. Tests of internal consistency of the instruments scored highly. A further 100 patients with acne and 50 controls completed all three instruments. The overall UKSIP mean score of patients was 5.6 (sd = 4.7) and of controls was 0.45. The ADI mean patient score was 40.3%, controls 17.6%. The CADI mean patient score was 42.1%, controls 13.2%. The CADI was the only instrument that correlated with the clinical acne severity score (p < 0.05); the UKSIP score correlated with the CADI score (p < 0.05) but not with the ADI score. This study has established aspects of the reliability and validity of the UKSIP, the ADI and the CADI.