A systematic review is a comprehensive literature search and synthesis project that tries to answer a well-defined question using existing primary research as evidence. A protocol is used to plan the systematic review methods prior to the project, including what is and is not included in the search.
Systematic reviews are often used as the foundation for a meta analysis (a statistical process that combines the findings from individual studies) and to re-evaluate clinical guidelines.
Systematic review and meta analysis are both types of evidence synthesis methods. Read more about evidence synthesis on the Types of Reviews page of this guide.
The figure1 below gives a high-level overview of the stages of the meta-analysis process. Related evidence synthesis methods may omit steps in the meta-analysis process; for example, systematic reviews will not include Step 14 meta-analyze.
Note the iterative nature of the process as search updates are conducted later in the project at Step 13 (an arrow on the left connects to Step 6 de-duplicate).
While this figure highlights appraisal of relevance in Steps 7 (screen abstracts) and 9 (screen full text), guidelines recommend critical appraisal of the individual study's validity and results once it is selected for inclusion.
1Tsafnet, G., Glasziou, P., Choong, M.K., et al. Systematic review automation technologies. Systematic Reviews 2014; 3:74; http://www.systematicreviewsjournal.com/content/3/1/74.