Conceptualisation, development and validation of T-QoL© (Teenagers’ Quality of Life): a patient-focused measure to assess quality of life of adolescents with skin diseases

Abstract

Aim

To develop and validate a dermatology-specific quality of life (QoL) instrument for adolescents with skin diseases.

Methods

Qualitative semi-structured interviews were conducted with adolescents with skin disease to gain in-depth understanding of how skin diseases affect their QoL. A prototype instrument based on the themes identified from content analysis of interviews was tested in several stages, using Classical Test Theory (CTT) and Item Response Theory (IRT) models to develop this new tool and conduct its psychometric evaluation.

Results

Thirty-three QoL issues were identified from semi-structured interviews with 50 adolescents. A questionnaire based on items derived from content analysis of interviews was subjected to Rasch analysis: factor analysis identified three domains, therefore not supporting the validity of T-QoL as a unidimensional measure. Psychometric evaluation of the final 18-item questionnaire was carried out in a cohort of 203 adolescents. Convergent validity was demonstrated by significant correlation with Skindex-Teen and CDLQI or DLQI. The T-QoL showed excellent internal consistency reliability: Cronbach's α=0.89 for total scale score and 0.85, 0.60, and 0.74 respectively for domains 1, 2 and 3. Test-retest reliability was high in stable subjects. T-QoL showed sensitivity to change in two sub-groups of patients who indicated change in their self-assessed disease severity.

Conclusion

Built on rich qualitative data from patients, the T-QoL is a simple and valid tool to quantify the impact of skin disease on adolescents' QoL; it could be used as an outcome measure in both clinical practice and clinical research.

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