Understanding systematic reviews and meta-analysis

This article is published as part of Impact with kind permission from BMJ Publishing Group. The article appears here in full. Health care professionals are increasingly required to base their practice on the best available evidence. In the first article of the series, I described basic strategies that could be used to search the medical literature (Akobeng, 2005a). After a literature search on a specific clinical question, many articles may be retrieved. The quality of the studies may be variable, and the individual studies might have produced conflicting results. It is therefore important that health care decisions are not based solely on one or two studies without account being taken of the whole range of research information available on that topic. Health care professionals have always used review articles as a source of summarised evidence on a particular topic. Review articles in the medical literature have traditionally been in the form of “narrative reviews” where exp