The ENDOCARE questionnaire (ECQ): a valid and reliable instrument to measure the patient-centeredness of endometriosis care in Europe

background: Endometriosis is prevalent and women need high-quality care, which should be patient-centered. This study aimed to develop a valid and reliable patient-centeredness questionnaire, based on a defined concept of patient-centered endometriosis care (PCEC). methods: A literature review, focus groups (FGs) with patients and an expert panel defined PCEC with 10 dimensions. The ENDOCARE questionnaire (ECQ) was developed. FGs resulted in 43 specific statements covering the 10 dimensions of PCEC, for which the ECQ measured ‘importance’ and ‘performance’. Medical and demographic questions and an open question were added. The Dutch ECQ questionnaire was piloted and reciprocally translated into English and Italian. Patients with endometriosis from Belgium, The Netherlands, Italy and the UK were invited to complete the ECQ online. Item analysis, inter-item analysis and confirmatory and exploratory factor analyses (EFA) and reliability analysis were performed. The theory-driven dimensions were adapted. results: The ECQ was completed by 541 patients. Based on item analysis, five statements were deleted. Factor analysis was performed on 322 questionnaires (only from respondents with a partner). Insights from the data-driven EFA suggested adaptations of the theory-driven dimensions. The reliability statistics of 9/10 adapted theory-driven dimensions were satisfactory and the root mean square error of approximation was good.