Development and preliminary validation of the Adolescent Psoriasis Quality of Life instrument: a disease-specific measure of quality of life in adolescents with psoriasis

Background No age-appropriate and disease-specific instrument currently exists to measure health related quality of life in adolescents with psoriasis (patients aged. 12-17 years). Objectives To develop and provide preliminary validation of the Adolescent Psoriasis Quality of Life instrument. Methods Qualitative interviews with adolescents with psoriasis, parents of adolescents with psoriasis, and healthcare professionals informed the development of an initial item pool for the instrument, which was subsequently refined through cognitive interviews. Finally, data from an independent sample of adolescents with psoriasis (n = 50) were used for item reduction, scale construction and initial validation, using a combination of techniques from classical test theory and Rasch modelling. Results Rich qualitative data concerning health related quality of life in adolescents with psoriasis (from 18 adolescents, 14 parents and four healthcare professionals), combined with cognitive interview testing (n = 12), resulted in a 41-item draft version. Item reduction led to the final version, a 17-item instrument consisting of two subscales showing good fit to their respective Rasch models: psy chosocial impact (12 items) and the impact of physical symptoms and treatment (five items). All a priori stated hypotheses regarding construct validity were supported. Both subscales and the total scale showed acceptable test-retest reliabilities (intraclass correlations 0.97, 0.89 and 0.96) and internal consistencies (Cronbach's alpha 0.94, 0.81 and 0.95). Conclusions The preliminary form of the Adolescent Psoriasis Quality of Life instrument shows promising psychometric properties. It can be used in daily clinical practice and research to support a patient-centred approach and inform treatment planning.