What randomized trials and systematic reviews can offer decision makers.

It is important to recognize the studies that yield the most reliable evidence upon which to base treatment decisions. Randomized trials have a particular place in providing high-quality unbiased comparisons of different treatments, when carried out to a high methodological standard. Empirical evidence shows that such trials are not always done well, and also that poor methodology is associated with biased findings. Consumers of the published literature need to be able to recognize which trials can be trusted. Systematic reviews and meta-analyses offer an organized approach to assessing all the relevant literature on a topic, particularly when several randomized trials address the same treatment comparison. Like trials, systematic reviews and meta-analyses need to be carried out to a high standard. They offer particular potential for providing the most useful information for clinical decision making. Critical aspects of these types of study are considered in this paper.