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Systematic Reviews: How do you perform a systematic review?

Introducing the topic

Every research project requires some preparation, and systematic reviews are no different. In most research projects, a general topic is chosen and then background information collected on that subject to develop expertise. The topic is then refined to create a research question, which can be investigated. The main difference is that when performing a systematic review, the topic is usually dictated by a health scenario in which there is a clinical need involved. After this step in the research process, searching for a systematic review and performing a systematic review differ.

Setting up the review criteria

Systematic reviews are the top level of evidence-based information. As such, the methodology for performing a systematic review has to be meticulous. To ensure that the methodology is adhered to, the protocols involved in generating a systematic review should be put in place in advance to alleviate any potential concerns about the validity of results. These guidelines are often published prior to starting the review as a way of being held accountable for the integrity of the process. These predetermined criteria should be designed to ensure the following:

  • Experts in the field are performing the review
  • Potential bias or conflict of interest is reduced or even eliminated
  • Studies that maybe be used are evaluated and appropriate for the review

For a complete overview of the standards that should be used when setting up the systematic review criteria, look at the website created by the Institute of Medicine.

Searching the literature

Once all the guidelines are in place, it is time to look for studies that not only answer the clinical or research question, but also fit the criteria. To find these studies, the reviewer will have to look through all the available databases that potentially covers the topic. There are several subject guides available that provide lists of the health databases available through APSU. 

Finding unpublished studies (the grey literature)

After looking for any matching studies in the databases, the reviewer should then look outside of the traditional databases for any published or unpublished studies that match the guidelines. These non-traditional sources are often referred to as grey literature. They often maintain research that was discarded for various reasons. As a result they may have study results that are at odds with the published literature. These studies then need to be examined to determine whether they should be included in the systematic review. Finding these studies can be difficult, but there are a few online resources that can be used to discover this type of unpublished research.

  • Google Scholar - This resource finds a lot of papers and studies that are kept at academic institutions.
  • The Grey Literature Report - This is a resource that is produced by the New York Academy of Medicine.
  • OpenGrey - This search engine looks through unpublished resources that can be found in Europe.

Evaluating each study

Once the studies for the review have been selected, they need to be evaluated. This part of the process involves appraising each of the studies to ensure their research matches the preset criteria of the review, they follow the laid out methodology for the review, and the results can be validated to be accurate. Evaluating these studies reduces the risk of bias in each of stage of the review, and promotes higher standards for the information produced.    

Extracting information from the studies

The next step in the review process is to extract the information from the studies that were selected and then evaluated for the systematic review. Extracting the results from these individual studies is a matter of collecting the relevant citation information, details regarding the participants studied, information about the intervention and comparisons, and the outcome results. This part of the process can be confusing and complicated; however, there are a number of tools for the various study types that can be used to help the reviewer collect the information. 

Synthesizing the data

Once the information has been extracted from the studies, the data is analyzed and then summarized. The summary should include an answer to the question posed by the review. Included in the summary is an overview of the similarities and inconsistencies in the included studies, a quantification of their differences, how that may have impacted the review, an estimate of the results being reviewed, and how accurate the estimate is. Since there are a variety of question types that can be covered by a review, and each type of questions uses different study types to find answers, the information processed and synthesized may vary. 

Writing the results

After the review process has been completed, the results have to be written. The systematic review has to include an explanation of the methods used to perform the review, how these methods were chosen, the search techniques used for finding the studies that were included in the review, and how the evaluation and assessment process for resources was managed. Included in the write up is an explanation regarding studies that were excluded from the review, the results of an analysis of the included studies, how the results of this analysis can be interpreted, as well as any recommendations that can be made as a result of the review should then be recorded.  

About this guide

This guide is not intended to be a comprehensive explanation of how to perform a systematic review. This is an overview of the steps involved in the process. For a more comprehensive breakdown of creating a system review, please look at the resources listed on the Tools and Resource page