... terms of the strength of the study designs, we considered RCTs best, followed by non-randomized controlled trials and observational studies. We assessed the quality and consistency of the best ... important contributors to the literature, but they became observational studies after the period of randomization ended, and are thus subject to the limitations of any observational study. The losses ... Only half of the cross-sectional studies used multivariate techniques to adjust for the effects of potential confounders, an omission that limited the value of these studies. Another concern was...