The Differences between Evidence Synthesis vs a Systematic Review

Evidence synthesis refers to any method that helps in identifying, collecting, and combining results from multiple studies. Evidence synthesis is a tool used by researchers, healthcare professionals, and policymakers to make crucial healthcare and policy decisions. We often hear about exciting new findings in drug development or clinical practice through various trials and studies. However, we mustn’t use findings from a single study, or piece of evidence, to make decisions. One study on its own can be inaccurate or misleading. The results of a study are affected by the study setting, the involved participants, and the environment around which the study was done. These factors vary from study to study and affect the study results to some degree. They are in most studies referred to as cofounders. High-quality studies will report on data of outcome measures after adjusting for these cofounders. By using evidence synthesis we can base our views and decisions on evidence collected from multiple studies.

Evidence synthesis, therefore, is a way of compiling information from multiple studies that have been conducted on the same topic and coming to an overall understanding of the results. Decisions made using these results are then more reliable. There are many types of methods used in evidence synthesis. Some of the most common review types include literature reviews, systematic reviews, scoping reviews, and meta-analyses. To learn more about the difference between a systematic review and scoping review you can read here. All the review types mentioned above attempt to summarize findings collected from different studies. Please note that review types that come under evidence synthesis should not be confused with peer reviews. The main aim of a peer review is to check the originality, quality, and validity of an individual study before it is published in a journal. Peer reviewers will also offer recommendations that can improve the quality of the study. To understand the difference between a peer review and a systematic review, you can click the link to learn more.

Systematic reviews have now become the pillar of evidence-based healthcare, and are the most popular form of evidence synthesis [1]. There are a number of steps in a systematic review that need to be followed completely. The rigorous, and transparent methodology involved in a systematic review has led to their growing popularity in healthcare, pharmacovigilance, and guiding policy development. The type of evidence review and synthesis method to be used will depend on the research question or topic it seeks to address.

Types Of Evidence Synthesis Methods

Let’s look at some of the different types of evidence synthesis methods in further detail.

Narrative Or Traditional Literature Reviews

A narrative or a traditional literature review is a comprehensive and objective analysis of the available literature on a particular topic. They are an essential component of the research process and help in providing context or a theoretical framework for your research. The main aim of a narrative review is to help deepen understanding by carefully analyzing available research on that subject. It should be noted that although it is a comprehensive analysis of the available literature, it is not exhaustive. Literature reviews are not exhaustive since they do not focus on one specific research question. They are advantageous though, in that, they provide a broader view of the topic of research. Narrative reviews can help answer broad questions, provide context or background information, and identify knowledge gaps by studying the existing literature.

Systematic Review

A systematic review employs explicit, transparent, and reproducible methods to identify, collect, and synthesize results from multiple studies. It involves the formulation of a highly specific research question. Then through a rigorous, and pre-specified methodology, it seeks to collect high-quality data from multiple sources to answer this question. Since it uses all of the currently available research on a topic, it is classified as a secondary research method (research of research). The results of a systematic review are used as high-quality evidence to support crucial decision-making.

Meta-analysis

Meta-analysis refers to the statistical analysis of data collected from individual studies on the same topic and aims to generate a quantitative estimate of the studied phenomenon, such as the effectiveness of an intervention [2]. The goal of any meta-analysis is to provide an outcome estimate that is representative of all the study-level findings. Meta-analytic methods permit researchers to quantitatively appraise and synthesize outcomes across studies to establish statistical significance and relevance in the outcome under study. In most meta-analyses, a forest plot or funnel plot is used. Data on the effect of the measure across studies are combined to provide a general view of the effect of the measure. The reporting of the intervention effect should be expressed in the same manner, across all the included studies.
A meta-analysis can be used alone or in combination with a systematic review, to synthesize the same studies. The use of these two methods together increases the quality of results.

Scoping Review

It is a relatively new approach to synthesizing research evidence. As such a definitive study design or procedure has not been developed for it, as yet. Scoping reviews are effective tools used to determine the scope of coverage of a body of literature on a certain topic. It aims to map the existing literature in a particular research area, in terms of volume, nature, and characteristics of the primary research. They are undertaken to summarize and disseminate research findings; and provide an opportunity to identify key concepts, gaps in the research; and types and sources of evidence to inform practice, policymaking, and research [3].

Conclusion

Systematic reviews are therefore one of the many different methods used to conduct evidence synthesis. There are various other review types available to synthesize existing evidence, each with its own benefits and limitations. The type of review used depends on the research question, scope, and intended application of the research.

References

1. Aromataris E, Pearson A. The systematic review: an overview. AJN. Am J Nurs. 2014;114(3):53–8.
2. Gopalakrishnan, S., and Ganeshkumar, P. (2013). Systematic reviews and meta-analysis: understanding the best evidence in primary healthcare. J Fam. Med. Prim. Care 2, 9–14. doi: 10.4103/2249-4863.10993.
3. Enhancing the scoping study methodology: a large, inter-professional team’s experience with Arksey and O’Malley’s framework. Daudt HM, van Mossel C, Scott SJ. BMC Med Res Methodol. 2013 Mar 23; 13():48