Reliability of skin-type self-assessment: agreement of adolescents' repeated Fitzpatrick skin phototype classification ratings during a cohort study

Background The Fitzpatrick Skin Phototype Classification (FSPC) is the most commonly used measure of skin type. In questionnaire-based surveys, self-rated FSPC is often used as a measure of respondents skin type. Objective The objective of this analysis was to assess test-retest reliability of the self-rated FSPC within a 12-month cohort study that examined the psychological sequelae of acne. Methods Participants were students aged 1417 years in four Australian secondary schools; two-government system schools and two private schools. The primary outcomes were a number of psychological measures. The FSPC was assessed by a single concise questionnaire item. Test-retest agreement (as measured by quadratic weighted kappa) of participants self-rated FSPC at three time-points (baseline, 6 and 12 months) was calculated. Results Of the 244 participating students, 209 students (86%) completed all three rounds of data collection. A further 26 students (11%) completed two rounds. Quadratic weighted kappa for Rounds 1 and 2 was 0.757 (95% CI 0.6630.831). For Rounds 2 and 3 it was 0.805 (95% CI 0.6590.893). Between Rounds 1 and 3 it was 0.767 (95% CI 0.6980.832). This represents good-to-very-good agreement. Skin type was retained as an independent variable in 8 of the16 regression models built to explain psychological outcomes in this study. Conclusion Skin type appears to be a significant factor in psychological morbidity in acne. The FSPC is a reliable method for assessing skin phenotype, even when elicited via a concise questionnaire item suitable for assessing skin type as a potential confounder in studies of other outcome factors.