Validity of self-reported endometriosis and endometriosis-related questions in a Swedish female twin cohort

Objective To examine the validity of self-reported endometriosis and to improve the reliability of questionnaires by including endometriosis-related questions. Design Analysis of survey questionnaire data. Setting Cross-sectional study. Patient(s) Cohort of 26, 898 female twins aged 20–60 years at interview, who participated in either of two surveys (1998–2002 or 2005–2006). Intervention(s) None. Main Outcome Measure(s) Endometriosis diagnosis in the Swedish National Inpatient Registry (IPR). Result(s) The self-reported endometriosis diagnoses and endometriosis-related questions from a nationwide population-based twin registry were linked with the IPR. Fairly good agreement was found between the self-reported and IPR data on endometriosis. The receiver operating characteristics (ROC) curves showed fairly good predictive ability of self-reported endometriosis to have a confirmed endometriosis diagnosis in the IPR with an area under the curve (AUC) 0.79 (95% confidence interval [CI], 0.77–0.81). Further, the predictive ability increased to AUC 0.89 (95% CI, 0.88–0.90) when there was additional information about infertility and age. Conclusion(s) Our results indicate that self-reported data on endometriosis are moderately accurate and may be useful in studies when register data are not available.