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Evidence Synthesis and Systematic Review Guide: Steps in the Evidence Synthesis Process

1. Formulate a Protocol

Creating a protocol for systematic reviews and scoping reviews allows you to plan or build the research plan for your project. It can be used as a guide or outline for your project. Depending on the type of evidence synthesis project and where it will be published, the protocol may also need to be registered. In particular, many journals require systematic reviews to have a protocol. There are different templates and resources for protocol creation and registration. Some are listed below.

Additional Resources and guidance (for systematic review protocols)

 

2. Create a Research Question

One of the most important steps in the evidence synthesis process is developing your research question. This will most logically occur after you have determined a knowledge gap in your area of research and you are focusing on answering a specific question. To be successful, the research question that you create should be well defined, clear, and appropriate in scope. The question is the foundation of your synthesis and your research team will use it to identify 2-5 potential search concepts. These search concepts will later be used in creating your search strategy. 

The video below from the University of Melbourne provides an overview of the process of developing a solid research question.

3. Choose Databases

Librarians can assist you in finding appropriate databases for your evidence synthesis project. Your research question and discipline will help to guide your decision in choosing relevant databases. To see a full list of our databases you can consult the All Databases A-Z list. Also you can consult the Subject Guides link for a list organized by topic or discipline. 

Each database is works differently. A librarian can assist you in creating complex searches based on the specialized syntax for the individual databases as well as translating those searches between databases. For more information or to complete the consultation form, visit the Scholar Services page.

4. Consult Grey Literature

Grey Literature: What's the point?

In evidence synthesis, it is beneficial to consider literature outside of the academic journals as well.

  • Grey literature can provide data that is not available in databases within commercial publishing venues. 
  • It can provide a platform for reporting the results of studies that may not be published because of null or negative results. 
  • For this reason grey literature can help to reduce publication bias, making reviews more comprehensive, timely, and balanced.

Paez A. Gray literature: An important resource in systematic reviews. J Evid Based Med. 2017;10(3):233-240. doi:10.1111/jebm.12266

Gray Literature Defined

"Grey (or gray) literature is literature produced by individuals or organizations outside of commercial and/or academic publishers. This can include information such as government reports, conference proceedings, graduate dissertations, unpublished clinical trials, and much more.  The sources you select will be informed by your research question and field of study, but should likely include, at a minimum, theses and dissertations."

https://guides.library.cornell.edu/evidence-synthesis/grey-literature 

Grey Literature Source Examples:

Proquest Dissertations and Thesis

Think Tank Search 
 

 

Write a Search Strategy

Search Strategy Basics

Another major piece of the evidence synthesis process is writing a search strategy. It is a best practice to work with a librarian on creating the search strategy since they will have advanced knowledge of the article databases.

Boolean Logic is also an important consideration when creating your search strategy. 

  • AND  helps to narrow your search
  • OR broadens a search
  • Not excludes a word or words from the search
  • adding an astract (*) at the root of the word helps to find all of the varients
  • Parantheses around a group of words allows them to be searched as a phrase
  • Adding quotes to a phrase allows for a search of the exact phrase


Sample Search Strategy (Agriculture Example)

(Information adapted from Cornell University: https://guides.library.cornell.edu/evidence-synthesis/search-strategy)

Citation Management Software for ES

Citation management tools like Endnote and Zotero can be invaluable to your evidence synthesis project. These tools can help you format your citation, deduplicate articles, and more. 

See the following link to learn more about citation management tools.

Screening Your Articles

During the article screening process team members first review the title and abstracts based on the inclusion and exclusion parameters to determine if they relate to the research question. After this process the full articles will need to be reviewed to determine if the study should be included based on your eligibility criteria.  

Some commonly used tools for managing this process include the following: 

  • Covidence
  • Rayyan
  • Excel

Risk of Bias Assessment

The Risk of Bias Assessment is used to enusre transparency and eleminate biases. It is usually applied to each individual study in a systematic review. Scoping reviews are not required to be evaluated for risk of bias.

Extraction of Data

It is important to create a well formulated plan for extracting your data. You should also do a "pilot" to test your strategy for extracting your data. There are many tools that can be used for data extraction including Covidence, RevMan, Excel, Systematic Review Data Repository, and others.

Synthesize, Map or Describe Results

Once the data extraction process has been completed, the findings will need to be presented through various means such as meta-analysis or descriptive synthesis.

The document provided below from the University of South Australia gives a details on data synthesis.

(Selected content for section on "Steps in ES" adapted from: A Guide to Evidence Synthesis: Cornell University Library Evidence Synthesis Service)

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