Levels of evidence in the urological literature

Purpose: The concept of levels of evidence is one of the guiding principles of evidence based clinical practice. It is based on the understanding that certain study designs are more likely to be affected by bias than others. We provide an assessment of the type and levels of evidence found in the urological literature. Materials and Methods: Three reviewers rated a random sample of 600 articles published in 4 major urology journals, including 300 each in 2000 and 2005. The level of evidence rating system was adapted from the Center of Evidence Based Medicine. Sample size was estimated to detect a relative increase in the proportion of studies that provided a high level of evidence (I and II combined) from 0.2 to 0.3 with 80% power. Results: Of the 600 studies reviewed 60.3% addressed questions of therapy or prevention, 11.5% addressed etiology/harm, 11.3% addressed prognosis and 9.2% addressed diagnosis. The levels of evidence provided by these studies from I to IV were 5.3%, 10.3%, 9.8% and 74.5%, respectively. A high level of evidence was provided by 16.0% of studies in 2000 and by 15.3% in 2005 (p = 0.911). Conclusions: This study suggests that a majority of studies in the urological. literature provide low levels of evidence that may not be well suited to guide clinical decision making. We propose that editors of leading urology journals should promote awareness for this guiding principle of evidence based clinical practice by providing a level of evidence designation with each published study.