**7. Results and statistical analysis**

A non-parametric statistic is opted because (1) there is no '*a priori reason*' to assume a particular disease model and (2) the assignment of the status '*unaffected*' is problematic because a surgical procedure is required to exclude endometriosis.

Allele and genotype frequencies were compared in the patient and control groups. The odds ratio (OR) was used to measure the strength of the association between the frequencies of allele and genotype and endometriosis. The software MedCalc (version 7.4.3.0) was used for statistical analyses. All 'p' values two-tailed and 95% Confidence Intervals (CI) were calculated.
