Applicability
In patient selection, 40 studies gave low concern, with 63 and 22 giving unclear or high risk respectively. An unclear or high risk was attributable to the two-gate selection of controls, or the study likely to only classify a limited spectrum of disease (tertiary centres or infertility clinics).
In regard the reference standard, 97 studies showed a low concern. Studies in the database/self-reporting group were deemed high/unclear depending on whether additional coding input for surgery was recorded.