What is a Systematic Review?
Systematic a: methodical in procedure or plan <a systematic approach> <a systematic scholar> b: marked by thoroughness and regularity <systematic efforts>
Review a: a retrospective view or survey (as of one's life) b: renewed study of material previously studied (2) : an exercise facilitating such study
"A systematic review attempts to collate all empirical evidence that fits pre-specified eligibility criteria to answer a specific research question. It uses explicit, systematic methods that are selected to minimize bias, thus providing reliable findings from which conclusions can be drawn and decisions made. Meta-analysis is the use of statistical methods to summarize and combine the results of independent studies." - Cochrane Collaboration
A Brief Introduction to Evidence-Based Medicine
The following image represents the hierarchy and availability of the different types of research evidence and studies. As you can see, Systematic Reviews and Meta-Analysis are the highest level of evidence, but the least populous of all the study types.
View the following presentation for a brief introduction to the EBM Cycle
Guidelines for strict clinical systematic reviews do not always work well for the fields of nutrition, public health or mental health. It is worthwhile, however to be familar with those guidelines and then modify the searching and the types of studies included to fit these disciplines. See the Guides for Writing Systematic Reviews box to the left.
There are guides for systematic reviews in non-clinical topics such as nutrition and public health reviews. You can see these on one of our other systematic review guides, Systematic Reviews for Nutrition and Public Health.
How Long do They Take?
Remember the evidence pyramid and how few systematic reviews and meta-anaylses there are? This can be attributed to a few factors:
- Many topics do not have enough lower-level research completed to create a thorough SR
- Many topics do not lend themselves to "pure" SRs
- Requirements for SRs are stringent, causing many attempts to fall short in methodology
- High-quality SRs take a lot of TIME and effort.
The Cochrane Collaboration estimates about a year to complete the process, and this is often by teams of people working together on one review.