Systematic reviews search, appraise and collate all relevant empirical evidence in order to provide a complete interpretation of research results. Although conventional SRs are typically used in clinical research and social sciences, they have found application in various other subject areas for example in advertising, education, international development, public policy, ecology, environmental sciences, engineering and basic science research The first example of a systematic review was conducted in by James Lind, who published a paper that aimed to provide a concise and unbiased summary of evidence on scurvy 8 9.
Cochrane drew attention to the vital importance of randomized control trials in determining the effectiveness of health treatments. This led to a greater international emphasis on the need to improve research synthesis by policy makers, academics, and clinicians 3. Gradually, topic areas outside of healthcare also adopted SRs as a way of comprehensively and systemically summarizing existing research.
If you are considering embarking on a systematic review, there are several issues you need to contemplate if you wish to conduct one.
Protocols provide a complete detailed description of the process by which the review will be conducted. Registering the protocol reduces research bias, duplication of effort, resource waste, and provides greater transparency You must adopt a comprehensive, objective and reproducible search strategy to capture all relevant sources of evidence. In doing so, you can be confident of having incorporated all the appropriate material for the topic at hand.
Following the predefined eligibility criteria, you then need to analyze the screened search results to extract data from those publications that meet the inclusion criteria.
Ideally, these methodological steps should preferably be performed by two authors independently, one of which is a methodologist and the other a content area expert.
Summarizing the results of the included studies and interpreting their findings in the light of certainty of evidence and their applicability are the final steps of completing a systematic review.
You can also include a meta-analysis if applicable. Systematic reviews offer a number of benefits. For starters, they deliver a clear and comprehensive overview of available evidence on a given topic. Moreover, SRs also help identify research gaps in our current understanding of a field. They can highlight methodological concerns in research studies that can be used to improve future work in the topic area Lastly, they can be used to identify questions for which the available evidence provide clear answers and thus for which further research is not necessary The process of conducting systematic reviews, especially for new authors, will prove to be a worthwhile endeavour.
Authors refine their knowledge on the subject area of interest, develop new research ideas, and gain critical skills in synthesising existing literature. We hope that you have found this introduction to systematic reviews helpful. Additional information about SRs can be found on the Cochrane website. If you have any questions or observations, please feel free to comment below.
She has been actively involved in Cochrane since , primarily as a systematic reviewer, clinical advisor and in teaching, but also in translational and dissemination activities.
Since Tina has been the co-director of Cochrane Croatia. How do these findings from your review change what is known on the topic or question? Discuss what contribution this review makes and how your review answers or addresses the original question. Discuss any gaps found in the research. Make recommendations for needed research to address these gaps and the importance of addressing them. Discuss the overall strength of evidence in support of your original question strong, moderate or weak.
What makes a good systematic review and meta-analysis? See all library locations. University Libraries. Search this Guide Search. What is a Rapid Review? What is a Scoping Review?
What is a Mapping Review? What is a Meta-Synthesis? What is a Mixed Methods Review? What is an Integrative Review? What is an Overview of Reviews? What is a Review of Complex Interventions?
What is a Diagnostic Test Accuracy Review? What is a Network Meta-Analysis? What is a Living Systematic Review? Systematic Review vs. What is a Systematic Review? When is a Systematic Review the most appropriate study design?
The second column relates to the intervention groups and the third column to the control groups. The fourth column visually displays the study results.
The higher the percentage weight, the bigger the box, the more influence the study has on the overall results. The sixth column gives the numerical results for each study e. The diamond in the last row of the graph illustrates the overall result of the meta-analysis.
Interpretation of meta-analysis[ 4 ]. Thus, the horizontal lines represent individual studies. For example, the forest plot of the effectiveness of dexamethasone compared with placebo in preventing the recurrence of acute severe migraine headache in adults is shown in Figure 2. Forest plot of the effectiveness of dexamethasone compared with placebo in preventing the recurrence of acute severe migraine headache in adults[ 17 ]. The quality of a meta-analysis cannot be any better than the quality of the studies it is summarizing.
Make sure that the meta-analysis quantifies the size of the effect in units that you can understand. Subgroup analysis looks at the results of different subgroups of trials, e. This should be planned at the protocol stage itself which is based on good scientific reasoning and is to be kept to a minimum.
Thus, after the analysis, if changing makes little or no difference to the overall results, the reviewer's conclusions are robust. If the key findings disappear, then the conclusions need to be expressed more cautiously. Systematic reviews have specific advantages because of using explicit methods which limit bias, draw reliable and accurate conclusions, easily deliver required information to healthcare providers, researchers, and policymakers, help to reduce the time delay in the research discoveries to implementation, improve the generalizability and consistency of results, generation of new hypotheses about subgroups of the study population, and overall they increase precision of the results.
As with all research, the value of a systematic review depends on what was done, what was found, and the clarity of reporting. Even though systematic review and meta-analysis are considered the best evidence for getting a definitive answer to a research question, there are certain inherent flaws associated with it, such as the location and selection of studies, heterogeneity, loss of information on important outcomes, inappropriate subgroup analyses, conflict with new experimental data, and duplication of publication.
The quality of reporting of systematic reviews is still not optimal. In a recent review of systematic reviews, few authors reported assessing possible publication bias even though there is overwhelming evidence both for its existence and its impact on the results of systematic reviews.
Even when the possibility of publication bias is assessed, there is no guarantee that systematic reviewers have assessed or interpreted it appropriately. To overcome certain limitations mentioned above, the Cochrane reviews are currently reported in a format where at the end of every review, findings are summarized in the author's point of view and also give an overall picture of the outcome by means of plain language summary.
This is found to be much helpful to understand the existing evidence about the topic more easily by the reader. A systematic review is an overview of primary studies which contains an explicit statement of objectives, materials, and methods, and has been conducted according to explicit and reproducible methodology. A meta-analysis is a mathematical synthesis of the results of two or more primary studies that addressed the same hypothesis in the same way.
Although meta-analysis can increase the precision of a result, it is important to ensure that the methods used for the reviews were valid and reliable.
High-quality systematic reviews and meta-analyses take great care to find all relevant studies, critically assess each study, synthesize the findings from individual studies in an unbiased manner, and present balanced important summary of findings with due consideration of any flaws in the evidence.
Systematic review and meta-analysis is a way of summarizing research evidence, which is generally the best form of evidence, and hence positioned at the top of the hierarchy of evidence.
They objectively summarize large amounts of information, identifying gaps in medical research, and identifying beneficial or harmful interventions which will be useful for clinicians, researchers, and even for public and policymakers. Source of Support: Nil. Conflict of Interest: None declared. National Center for Biotechnology Information , U. J Family Med Prim Care. Gopalakrishnan and P. Author information Copyright and License information Disclaimer.
Address for correspondence: Dr. E-mail: moc. This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3. This article has been cited by other articles in PMC. Abstract Healthcare decisions for individual patients and for public health policies should be informed by the best available research evidence. Keywords: Evidence-based medicine, meta-analysis, primary care, systematic review.
Introduction Evidence-based healthcare is the integration of best research evidence with clinical expertise and patient values. The purpose of this article is to introduce readers to: The two approaches of evaluating all the available evidence on an issue i. Application What is the effect of antiviral treatment in dengue fever?
The purpose of these evidence maps is similar to scoping reviews to identify and analyse gaps in the knowledge base [ 37 , 38 ]. In fact, most evidence mapping articles cite seminal scoping review guidance for their methods [ 38 ]. The two approaches therefore have many similarities, with perhaps the most prominent difference being the production of a visual database or schematic i.
A further popular method to define and scope concepts, particularly in nursing, is through the conduct of a concept analysis [ 39 , 40 , 41 , 42 ].
There is limited methodological guidance on how to conduct a concept analysis and recently they have been critiqued for having no impact on practice [ 39 ]. In our opinion, scoping reviews where the purpose is to systematically investigate a concept in the literature offer a methodologically rigorous alternative to concept analysis with their results perhaps being more useful to inform practice. Comparing and contrasting the characteristics of traditional literature reviews, scoping reviews and systematic reviews may help clarify the true essence of these different types of reviews see Table 1.
Rapid reviews are another emerging type of evidence synthesis and a substantial amount of literature have addressed these types of reviews [ 43 , 44 , 45 , 46 , 47 ]. As such, a rapid review could potentially be conducted for any of the indications listed above for the scoping or systematic review, whilst shortening or skipping entirely some steps in the standard systematic or scoping review process.
There is some overlap across the six listed purposes for conducting a scoping review described in this paper. For example, it is logical to presume that if a review group were aiming to identify the types of available evidence in a field they would also be interested in identifying and analysing gaps in the knowledge base.
However, we have chosen to list them as discrete reasons in this paper in an effort to provide some much needed clarity on the appropriate purposes for conducting scoping reviews. As such, scoping review authors should not interpret our list of indications as a discrete list where only one purpose can be identified. It is important to mention some potential abuses of scoping reviews.
Reviewers may conduct a scoping review as an alternative to a systematic review in order to avoid the critical appraisal stage of the review and expedite the process, thinking that a scoping review may be easier than a systematic review to conduct.
Others may conduct a scoping review with very broad questions as an alternative to investing the time and effort required to craft the necessary specific questions required for undertaking a systematic review. In these cases, scoping reviews are not appropriate and authors should refer to our guidance regarding whether they should be conducting a systematic review instead.
This article provides some clarification on when to conduct a scoping review as compared to a systematic review and clear guidance on the purposes for conducting a scoping review.
We hope that this paper will provide a useful addition to this evolving methodology and encourage others to review, modify and build upon these indications as the approach matures. Further work in scoping review methods is required, with perhaps the most important advancement being the recent development of an extension to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses PRISMA for scoping reviews [ 48 ] and the development of software and training programs to support these reviews [ 49 , 50 ].
Researchers may preference the conduct of a scoping review over a systematic review where the purpose of the review is to identify knowledge gaps, scope a body of literature, clarify concepts, investigate research conduct, or to inform a systematic review. Seventy-five trials and eleven systematic reviews a day: how will we ever keep up?
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