Strengths of this study included the consistent entry criteria, the use of histology and microbiology markers for upper genital tract disease, and the large number of women studied. Weaknesses included the lack of a purely unaffected control and the lack of a laparoscopic diagnosis for PID. Women with objective evidence of PID were compared with women in the same cohort who had no evidence of the disorder, all of whom had signs and symptoms consistent with PID. This made it unlikely that women would be selected in a biased fashion) for this study because the outcome was actual upper genital tract disease. Furthermore, both control subjects such as those used in the current study and asymptomatic “external” control subjects gave similar results. Therefore, the authors think it unlikely that their results, comparing clinically similar women, are spurious. The authors also regarded laparoscopic data as not compulsory because the histologic finding of endometritis has been well correlated with salpingitis in previous studies