A new instrument for assessing quality of life in atopic dermatitis: international development of the Quality of Life Index for Atopic Dermatitis (QoLIAD)

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Abstract
Background Atopic dermatitis (AD) is a chronic or chronically relapsing inflammatory skin condition that can have a considerable impact on those affected. There are a number of instruments available to measure outcome in dermatological conditions but none have been developed specifically for AD. In addition, most measure symptoms and/or daily functioning, which are potential influences on quality of life (QoL) rather than assessments of the construct itself. Objectives The aim of the current study was to develop a new instrument specifically designed to measure QoL in adults with AD—the Quality of Life Index for Atopic Dermatitis (QoLIAD). Methods The instrument was developed based on the needs‐based model of QoL and was produced in several different countries simultaneously. Its content was derived from 65 in‐depth interviews with relevant patients in the U.K., Italy and the Netherlands. The initial version of the measure was produced in U.K. English and translations were produced for the Netherlands, Italy, Germany, France and the U.S.A. using a dual translation panel methodology. A Spanish version was developed using the same adaptation process after the instrument was finalized. Field‐test interviews were conducted with approximately 20 patients in each country to assess face and content validity. The instrument [in addition to the Dermatology Life Quality Index (DLQI) and the Psychological General Well‐Being Schedule (PGWB)] was then administered to up to 300 AD patients in each country at two time points to finalize the instrument and test its psychometric properties. Results The initial version of the QoLIAD had 56 items that reflected the areas of need fulfilment identified in the qualitative interviews as having been affected by AD: mental and emotional stimulation, physical and emotional stability, security, sharing and belonging, self‐esteem, personal development and fulfilment. Comments from patients in field‐test interviews resulted in the removal of 14 items, to leave a 42‐item instrument that was considered relevant and acceptable. The number of patients participating in the survey were 286 in the U.K., 46 in the Netherlands, 213 in France, 187 in Germany, 178 in the U.S.A. and 83 in Spain. Application of the Rasch model to these data identified the final 25‐item QoLIAD. Unidimensionality was confirmed, with deviation of the total scale from the Rasch model evident at a single time point in one country only (the U.K.). All language versions, with the exception of the Dutch measure, had test–retest reliability coefficients in excess of 0·85. The test–retest in the Netherlands was 0·80. However, this country had the smallest sample size and the corresponding reliability for the DLQI was only 0·40. The QoLIAD had adequate internal consistency and the initial indications of construct validity were good. The levels of association with the DLQI indicated that the two instruments measure related but distinct constructs. Conclusions The QoLIAD is a practical, reliable, valid and culturally applicable instrument for measuring the impact of AD and its treatment on QoL in clinical trials or in routine clinical practice.