Evidence Synthesis

What is Evidence Synthesis?

Evidence synthesis (also commonly referred to as knowledge synthesis) is the attempt to systematically collate all pertinent information on a given topic to address a research question (1, 2).

While there are many different kinds of evidence syntheses (e.g. systematic reviews, health technology assessments, scoping reviews, etc.), most follow a similar pattern or structure:

  • Formulating a research question;
  • Establishing clear inclusion and exclusion criteria;
  • Identifying all potentially relevant studies and literature;
  • Applying the inclusion/exclusion criteria;
  • In some cases (e.g. for systematic reviews) assessment of the quality of studies; and
  • Summarizing and analyzing the evidence (3-5).

Examples of patient-oriented evidence syntheses in the research literature include:

Domecq JP, Prutsky G, Elraiyah T, Wang Z, Nabhan M, Shippee N, Brito JP, Boehmer K, Hasan R, Firwana B, Erwin P, Eton D, Sloan J, Montori V, Asi N, Dabrh AM, Murad MH. Patient engagement in research: a systematic review. BMC Health Serv Res. 2014 Feb 26;14:89. doi: 10.1186/1472-6963-14-89. Review. PubMed PMID: 24568690; PubMed Central PMCID: PMC3938901.

Kovacs Burns K, Bellows M, Eigenseher C, Gallivan J. 'Practical' resources to support patient and family engagement in healthcare decisions: a scoping review. BMC Health Serv Res. 2014 Apr 15;14:175. doi: 10.1186/1472-6963-14-175. PubMed PMID: 24735787; PubMed Central PMCID: PMC4005635.

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Why is Evidence Synthesis important?

Evidence syntheses are important for identifying, summarizing, and disseminating evidence which can otherwise get lost in the giant mass of health sciences literature.

Perhaps one of the most well-known examples of an evidence synthesis and the dramatic difference it can make in health care was a 1996 systematic review of randomized controlled trials (RCTs), in which corticosteroids were given to women in early labour. In the review, researchers found that corticosteroid treatment significantly reduced the odds of premature babies dying from preterm complications. The first RCT to show this was conducted in 1972, and by 1991, seven more trials had been reported. But many obstetricians did not realize the treatment was so effective. The review’s publication in 1996 saw a dramatic increase in the use of corticosteroids for women about to give birth too early. While this review was incredibly successful in changing practice and treatment, it also demonstrated that evidence for this treatment had already been in existence for several years, and could have prevented the death and suffering of many infants, had physicians known (6).

The following is an update of the original 1996 review:

Roberts, D., and S. Dalziel. "Antenatal Corticosteroids for Accelerating Fetal Lung Maturation for Women at Risk of Preterm Birth." The Cochrane Database of Systematic Reviews 3 (2006): CD004454. Web.
http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD004454.pub2/abstract

As this example shows, evidence syntheses are important for identifying, summarizing, and disseminating evidence which can otherwise get lost in the giant mass of health sciences literature. This example was so poignant in demonstrating the importance and necessity of conducting systematic reviews that the Cochrane Collaboration incorporated the results of this review into its logo, to illustrate “just one of many examples of the human costs resulting from failure to perform systematic, up-to-date reviews of RCTs of health care – and the powerful impact of evidence on guidelines, on practice, and on mortality rates” (6).

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When do you do an Evidence Synthesis?

There are several reasons why someone might conduct an evidence synthesis. Here are some of the most common ones:

  • To summarize a body of research literature that has not yet been synthesized, or which might be better synthesized;

  • To identify gaps or biases in the literature where more research needs to be conducted or where the quality of studies needs to be improved before conclusions can be drawn; and

  • To provide a strong background or context upon which to base future research (7).

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How do you do an Evidence Synthesis?

This is a great introductory video on systematic reviews (including meta-analysis), the stages involved in conducting a systematic review, and how to evaluate them. While this video is focused on systematic reviews, it is still relevant to other types of synthesis.

Khan, Khalid S et al. “Five Steps to Conducting a Systematic Review.” Journal of the Royal Society of Medicine 96.3 (2003): 118–121. Print. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC539417/

This article takes the reader through each of the steps for conducting a systematic review, using a review on public water fluoridation as an example. Again, while this is specific to systematic reviews, many of the steps are directly transferable to other forms of synthesis.

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How does MSSU support Evidence Synthesis?

To share our expertise in Evidence Synthesis, we:

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References

  1. Higgins JPT, Green S, Cochrane C. Cochrane handbook for systematic reviews of interventions. Chichester, England; Hoboken, NJ: Wiley-Blackwell; 2008.

  2. Kastner M, Tricco AC, Soobiah C, Lillie E, Perrier L, Horsley T, et al. What is the most appropriate knowledge synthesis method to conduct a review? Protocol for a scoping review. BMC Med Res Methodol. 2012;12:114.

  3. Grimshaw J. A Guide to Knowledge Synthesis. Canadian Institutes of Health Research; 2010 [cited 2014].

  4. Booth A, Papaioannou D, Sutton A. Systematic approaches to a successful literature review. Thousand Oaks, CA: Sage Publications; 2012.

  5. Khan KS, Kunz R, Kleijnen J, Antes G. Five steps to conducting a systematic review. Journal of the Royal Society of Medicine. 2003;96(3):118-21.

  6. The Cochrane Collaboration. The story of the Cochrane logo. 2013 [cited 2014 Dec 29].

  7. Kitchenham B. Procedures for performing systematic reviews. Keele, UK, Keele University. 2004;33:2004.

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