Questionnaire items to assess skin color and erythemal sensitivity: reliability, validity, and "the dark shift".

BACKGROUND Skin pigmentation is a key factor for UV radiation exposure related cancers. To appropriately target cancer control activities related to this exposure and for better representation in epidemiologic studies, a valid and reliable assessment of skin color is required. METHODS The validity and reliability of two self-report measures were assessed: skin color and erythemal sensitivity. A sample of 289 university students categorized their unexposed skin color and photosensitivity via a questionnaire. Skin color was also measured by spectrophotometer. After 7 days, participants repeated the self-report assessment. RESULTS Significant correlations were found for both self-report items with objective measures, indicating that these items may be valid assessment tools (color: Spearman's rho=-0.75, P<0.001; photosensitivity: Spearman's rho=-0.64, P<0.001). No sex differences in validity were evident. Stronger correlations were found among those of European than those of non-European ethnicity (color: Spearman's rho=-0.78 versus -0.59, bootstrap P=0.007; photosensitivity: Spearman's rho=-0.63 versus -0.28, bootstrap P=0.001). Strong biases toward overestimation of skin pigmentation were evident, ranging from 36% in the self-identified fair skin group to 77% in the medium skin color group. Intrarater reliability of the questionnaire items was high (color: k=0.78, P<0.001; photosensitivity: k=0.77, P<0.001). CONCLUSIONS Study findings suggest that self-report may be a valid measurement strategy when assessing skin type, but there is a bias toward overestimation of skin color and, potentially, UV radiation resilience. IMPACT This bias has the potential to undermine the effectiveness of skin cancer prevention efforts and needs to be addressed in health promotion programs.