Cross-Cultural Equivalence of the Patient- and Parent-Reported Quality of Life in Short Stature Youth (QoLISSY) Questionnaire

Abstract

Background: Testing cross-cultural equivalence of Patient Reported Outcomes requires sufficiently large samples per country, which is difficult to achieve in rare endocrine paediatric conditions. We describe a novel approach to cross-cultural testing of the Quality of Life in Short Stature Youth (QoLISSY) questionnaire in five countries by sequentially Taking-One-Country-Out (TOCO) from the total sample and iteratively comparing the resulting psychometric performance. Methods: Development of the QoLISSY proceeded from focus group discussions over pilot testing to field testing in 268 short statured patients and parents. In exploring cross-cultural equivalence the iterative TOCO technique was used to examine and compare validity, reliability and convergence of QoLISSY patient- and parent-ratings in the field test data set, and to predict QoLISSY scores from clinical, socio-demographic and psychosocial variables. Results: Validity and reliability indicators were satisfactory for each sample after iteratively omitting one country. Comparisons with the total sample revealed cross-cultural equivalence in internal consistency and construct validity for patients and parents, high inter-rater agreement and a substantial proportion of QoLISSY variance explained by predictors. Conclusion: The TOCO technique is a powerful method to overcome problems of country specific testing of PRO instruments. It provides an empirical support to QoLISSY´s cross-cultural equivalence and is recommended for future research.