A systematic review answers a defined research question by collecting and summarizing all empirical evidence that fits pre-specified eligibility criteria.
A meta-analysis is the use of statistical methods to summarize the results of these studies.
Systematic reviews, just like other research articles, can be of varying quality. They are a significant piece of work (the Centre for Reviews and Dissemination at York estimates that a team will take 9-24 months), and to be useful to other researchers and practitioners they should have:
clearly stated objectives with pre-defined eligibility criteria for studies
explicit, reproducible methodology
a systematic search that attempts to identify all studies
assessment of the validity of the findings of the included studies (e.g. risk of bias)
systematic presentation, and synthesis, of the characteristics and findings of the included studies
Not all systematic reviews contain meta-analysis.
Meta-analysis is the use of statistical methods to summarize the results of independent studies. By combining information from all relevant studies, meta-analysis can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review. More information on meta-analyses can be found inCochrane Handbook, Chapter 9.
A meta-analysis goes beyond critique and integration and conducts secondary statistical analysis on the outcomes of similar studies. It is a systematic review that uses quantitative methods to synthesize and summarize the results.
An advantage of a meta-analysis is the ability to be completely objective in evaluating research findings. Not all topics, however, have sufficient research evidence to allow a meta-analysis to be conducted. In that case, an integrative review is an appropriate strategy.