Endometriosis

To the Editor.— I would appreciate it if Cramer et al1could clarify some points regarding the methodology and conclusions of their case-control study on endometriosis. The first question concerns their use of infertility as the main symptom to select cases, since pain may actually be a more common symptom.2Second, since cases were older than controls and since ovulatory function declines with age, it seems the study apparently did not control for possible decline in ovulation (their menstrual cycle data notwithstanding). The infertility observed might therefore in some large part be age related, not endometriosis related. Third, some of the controls may have had endometriosis, and if these were to be eliminated, this would change some of the observed risk ratios, particularly relating to their observations on height and smoking before the age of 17 years, differences that seemed less firm to begin with. Fourth, their findings