Basics to understanding systematic reviews

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Systematic review myths

  1. Systematic reviews only include data from randomized controlled trials. Many systematic reviews only include RCTs but this statement is not true. Systematic reviews can also include data from non-randomized studies, especially for topics where trials are not ethically or practically possible or when there is very limited evidence available.

  2. Low level evidence means poor quality studies were included in the review. Much more goes into the certainty ratings of review findings than just the risk of bias or quality of the included studies.  Inconsistency, indirectness, imprecision, and publication bias are also taken into account.

  3. Reviews of the effectiveness and comparative effectiveness of interventions are the same. These are two different types of questions that warrant two different types of evidence. Effectiveness reviews include studies of the intervention compared to a placebo or no intervention. Comparative effectiveness reviews testing the effects of different active interventions. Ideally, the effectiveness of an intervention is established before evaluations of comparative effectiveness proceed, but in some cases a placebo or no intervention is not ethical so only active interventions can be compared. A systematic review trying to answer both comparative effectiveness and effectiveness questions can be challenging to conduct. 

  4. Systematic reviews answer overly narrow questions, and don’t answer my more complicated clinical question. Reviews carefully establish what is known for a defined segment of the evidence base for a clinical area, and these related reviews are intended to be brought together in an umbrella review to cover broader clinical practice questions or to be considered together by guideline groups that issue clinical recommendations.

  5. Systematic reviews that include only one or two studies are pointless.  Reviews are sometimes undertaken when there are only one or two published studies with rigorous evidence to answer the systematic review question. These reviews can be very important for helping those undertaking primary studies strengthen their methods and provide important study outcomes. Highlighting the need for new evidence in the research area can also stimulate funders and investigators to invest in the topic. 


Facts about our FRG Cochrane systematic reviews

  1. Our specialized literature searches will include results from several databases. This will usually result in thousands of titles and abstracts being screened for potential inclusion in the review.

  2. Each author team will include at least one content expert on the topic, and someone with systematic review methods expertise.

  3. Systematic reviews provide evidence-based answers to important clinical and policy questions, highlighting how much certainty should be assigned to those answers.  A range of stakeholders rely on systematic reviews to understand the existing evidence base and what new evidence is needed to improve health and clinical care for a range of topics.

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