The thesis is based on three papers on endometriosis, a relatively common chronic inflammatory gynecological disease which can cause significant pain and infertility. All three papers are based on cross-sectional data from postal surveys conducted among a randomly selected sample of women residing in Oslo and members of the Norwegian Endometriosis Association and the Oslo Rheumatoid Arthritis Registry. The main weakness of all three papers is possible selection bias.
The aim of the first paper was to evaluate the measurement properties of the Norwegian version of the disease-specific quality of life questionnaire Endometriosis Health Profile-30. The scale self-image of the Norwegian version EHP-30 does not seem to measure the construct self-image appropriately. Thus, for Norwegian quality of life studies on women with endometriosis, the EHP-30 must be used with caution.
The aim of the second paper was to compare quality of life in women with endometriosis and women with rheumatoid arthritis using the generic quality of life questionnaire Short form-36. Women with endometriosis seemed to have poorer mental quality of life compared with women with rheumatoid arthritis, despite similar pain scores.
The aim of the third paper was to identify predictors of endometriosis among factors commonly associated with endometriosis and available to physicians through medical interview. Further, if successful, to combine these to develop and internally validate a prediction model to aid primary care physicians in early identification of women at high risk of developing endometriosis. The predictors absenteeism from school due to dysmenorrhea and family history of endometriosis demonstrated the strongest association with disease. A prediction model based on these two predictors appears to be a relatively efficient screening tool for endometriosis.