Translation, adaptation, and validation of a questionnaire: The methodological process exemplified by the Croatian version of the ReproKnow questionnaire

Introduction: Questionnaires represent an important methodological tool in research and clinical practice. When using a questionnaire in a new linguistic and cultural context, in addition to linguistic translation, it is necessary to conduct its adaptation and validation. The aim of this study was to present the general methodological process of translation, adaptation, and validation of a questionnaire, which was then illustrated through the example of the Croatian version of the ReproKnow questionnaire, developed to assess the reproductive health knowledge of women with systemic autoimmune diseases. Participants and Methods: The study was conducted at the Division of Clinical Immunology and Rheumatology, University Hospital Centre Zagreb, from August 2023 to June 2025. In addition to the authors responsible for translation and adaptation, 30 physicians, 10 nurses/technicians, and 10 patients participated in validation of the questionnaire, while internal consistency was assessed on the responses of 100 patients. Results: The item content validity index (I-CVI) was high (0.90–1.00), with a scalelevel content validity index (S-CVI) of 0.98, and universal agreement (S-CVI/UA) of 0.80. Item clarity was also rated very highly (2.6–3.0 on a 1–3 scale). Comparison of the original and back-translated versions showed acceptable comparability of language (1.67–2.40; ref.