Levels of evidence in endoscopic research: a longitudinal survey

In clinical studies in surgical journals, the proportion of randomized trials is below 10%, and this has remained unchanged over the years. The problems of performing randomized studies in surgery are discussed, and we classify the publications in the only Medline journal aiming at gynecological endoscopy, The Journal of the American Association of Gynecological Endoscopy (JAAGL), according to the publication type and level of evidence over a recent time period, comparing the results with other surgical and general medical journals. The 1994–2002 volumes of the JAAGL are evaluated, as well as a limited number of issues of other leading journals on surgery, obstetrics-gynecology and general medicine. In the JAAGL issues from 1994 to 2002, most articles were based on therapeutic trials (549/862=64%). No significant changes occurred in the distribution of the different categories from 1994–2002. The number of randomized trials in this period is 48 (range: one to nine per year). Of 549 therapeutic clinical studies, the proportion of randomized trials is 8.8% (48/549). Of the 549 therapeutic studies, 432 case series without control groups (79%) were reported. In the endoscopic journal of the general surgeons and the general surgical journal, a similar distribution of publication types and levels of evidence can be seen. In the obstetrical-gynecological journal, 12 out of 22 therapeutic studies (44%) are based on randomized trials. In the journals of general medicine, randomized studies account for 74% of all the published studies. Case series without controls predominate in surgical journals, and the proportion of randomized trials has remained small over the years. Particularly in the fields of endoscopy and minimally invasive surgery with many emerging new techniques, the importance of randomized studies is stressed.