Vision-related quality of life in children: Cross-cultural adaptation and test-retest reliability of the Danish version of the paediatric refractive error profile 2.

PURPOSE: To translate and cross-culturally adapt PREP2 into Danish and to investigate the face validity and reliability of Danish PREP2 through cognitive interviewing, Rasch and reliability analyses.

METHODS: The Danish PREP2 was translated using a standardized procedure and then pretested following the Three-Steps-Interviews (TSTI) process. A total of 15 myopic children aged 7-14 wearing either orthokeratology lenses (ortho-k) or single-vision spectacles (SVS) were included in pretesting comprising cognitive interviews and Rasch analysis. Data from cognitive interviewing was analysed thematically according to Collins. Rasch analysis was used to pretest the psychometric properties in terms of person- and item-fit statistics. Reliability was assessed via test-retest using Intra-class correlation coefficient (ICC) in the CONTROL study population, which consisted of 60 Danish children aged 7-14 years wearing either ortho-k or SVS.

RESULTS: Fifteen children participated in pilot studies comprising of cognitive interviewing and Rasch analysis and 44 out of 60 CONTROL children participated in test-retest reliability analysis. The translation process resulted in a Danish version of PREP2 corroborating the original. Pretesting highlighted issues in the contextualization of items and in marking responses. Thus, we introduced a digital format with help texts. Cognitive interviewing identified issues in the following Collins' themes: comprehension (understanding of concepts), judgement (ambiguity of items) and response (selecting answers). Rasch analysis indicated that help texts were useful for clarifying context. The ICC was 0.77 (95% CI: 0.66-0.85).

CONCLUSIONS: The cross-cultural adaptation of PREP2 was satisfactory and issues were identified and corrected through pretesting. The test-retest reliability showed substantial consistency. The instrument could be validated in a more generalizable setting in future studies.

TRIAL REGISTRATION: NCT03246464 (CONTROL study).