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
In order to be thorough and systematic, multiple databases must be used and grey literature must also be searched if it is applicable. The Cochrane Collaboration recommends searching a minimum of three databases:
- The Cochrane Central Register of Controlled Trials
- MEDLINE (via PubMed or OVID)
- EMBASE (usually searched via Scopus)
The Cochrane Collaboration also specifies that:
- Searches should seek high sensitivity, which may result in relatively low precision.
- Too many different search concepts should be avoided, but a wide variety of search terms should be combined with OR within each concept.
- Both free-text AND subject headings should be used.
Your inclusion/exclusion criteria are extremely important and allow you to make your results more precise after you've conducted a search to find as much as you can that touches on your topic of interest.
Just as in clinical or bench research, a detailed methodology of your search strategy, results and inclusion/exclusion criteria must be included in your review so that it is reproducible. PRISMA standards require you to fill out a flow diagram and provides a helpful checklist to determine if your SR is complete.
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.