Background: Several instruments are available for assessing impairment and disability associated with psoriasis. The first true psoriasis-specific quality of life (QoL) questionnaire suitable for use in clinical trials, the Psoriasis Index of Quality of Life (PSORIQoL), has recently been developed in the UK. The aim of the current study was to produce and validate a conceptually equivalent US version of the PSORIQoL with equally good psychometric properties.
Methods: A lay translation panel was employed to ensure that the wording of the questionnaire was appropriate for a US population. Semi-structured interviews conducted with 37 patients tested the instrument's ease of completion, relevance and comprehensiveness. Finally, a test-retest validation mail survey was conducted with 72 patients to determine reliability, internal consistency and construct validity.
Results: Few changes were necessary to the wording of the questionnaire. Interviewees found the questionnaire easy to complete (requiring an average of 4 min) and the content relevant and comprehensive. The adapted measure had comparable psychometric properties to the original, with a test-retest reliability coefficient of 0.90, indicating excellent reproducibility. Internal consistency and initial indications of construct validity were also good, with scores on the measure related as expected to perceived general health and severity of psoriasis and the presence of visible lesions.
Conclusions: The US PSORIQoL is a practical, reliable and valid instrument for measuring the impact of psoriasis and its treatment on QoL in clinical trials and in routine practice. It remains necessary to establish the instrument's responsiveness to changes in QoL associated with effective interventions.