The results of a single trial/study can be misleading. Separate but similar small trials/studies can produce apparently conflicting results, often due to chance.
Collecting information from different trials/studies, using explicit and systematic methods in order to minimise bias, provides an objective and reliable way of answering a specific research question. By using a careful “study of studies”, called a systematic review, it is possible to distinguish the effects of treatment from the effects of chance.
Systematic reviews are an established part of research. They look at all trials/studies on a topic, not just selected studies which could result in biased conclusions. Often findings from separate but similar studies are combined to calculate an overall result. This process is called a meta-analysis.
Systematic reviews and meta-analyses are an important part of health research, because they can identify findings that might otherwise be missed in individual trials/studies.