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Knowledge Synthesis & Systematic Reviews

Part 1: Systematic Reviews: The Essentials

What is a Systematic Review?

What is a Systematic Review?


"Systematic reviews seek to collate evidence that fits pre-specified eligibility criteria in order to answer a specific research question. They aim to minimize bias by using explicit, systematic methods documented in advance with a protocol."

Key Characteristics

  • a clearly stated set of objectives with pre-defined eligibility criteria for studies
  • an explicit, reproducible methodology
  • a systematic search that attempts to identify all studies that would meet the eligibility criteria
  • an assessment of the validity of the findings of the included studies, for example through the assessment of risk of bias; and
  • a systematic presentation, and synthesis, of the characteristics and findings of the included studies

(Chapter 1: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.2 (updated February 2021). Cochrane, 2021. Available from

Common Review Types

Common Review Types

There are many different review types that can be used depending on your research question, disciplines, and the amount of time and resources you have.

Literature Review: An account of what has been published on a topic. They are written primarily by researchers working in the topic's area of study. A literature review illustrates what knowledge and ideas have been established on a particular topic, what the strengths and weaknesses are, and to identify controversies in the literature. Literature reviews also formulate questions for further research and inquiry.

Systematic Review:  A study of studies. These reviews aim to collect all existing evidence to address a specific research question. The criteria used to select included evidence is pre-defined and responds precisely to the research question. Explicit methods to minimize bias and increase transparency are used to produce reliable synthesis of information. The purpose of this synthesized information is to create strong evidence to inform clinical decision-making, policy and research.  

Scoping Review: Also known as mapping reviews, scoping reviews are exploratory research projects that systematically map the literature on a topic by identifying key concepts, theories and sources of evidence that inform practice in the field. The main objectives of scoping reviews are to identify gaps in the current research and highlight areas that require further inquiry. They aim to assess the potential size and scope of available research literature (often including ongoing research) and the current level of synthesis available. 

Rapid Review: A (condensed) study of studies. Rapid reviews are conducted using the same methods as in a systematic review. Rapid reviews differ from other review types because decisions about the process of conducting the review are centred on the time allotted for the completion of the review.  For example, the completeness of the initial search is determined by time constraints and/or the formal quality assessment is time-limited.

Umbrella Review: An umbrella review is a review of reviews. It compiles all the evidence from existing reviews on a topic to give a high level overview. An umbrella review is commonly conducted when there are multiple competing interventions for a condition. An overview of reviews about each of these interventions can be useful in determining how to best translate the evidence into practice. Like many other reviews, the aim of an umbrella study is to determine what is known on a topic, what remains unknown, and recommendations are made for what requires further research.

Critical Reviews: A critical review describes an author’s hypothesis or conceptual model based on key literature in their field of study. One of the aims of the critical review is to demonstrate that the reviewer has a commanding understanding of the literature to the point where they can extrapolate hypotheses on the topic of review. This type of review goes beyond the level of detailed description of the existing literature. While conducting a critical review, the reviewer identifies the most significant research in the field and evaluates the literature based on its contribution to the field (as opposed to a formal quality assessment). This review type is usually narrative or conceptual.

Additional Resources

A typology of reviews: an analysis of 14 review types and associated methodologies

Systematic Review Process

The Systematic Review Process


Step 1: Determine the Need for a Systematic Review

  • Has anyone already done one or are there any in process? Search Prospero for in-process reviews and PubMed for published review

Step 2: Assemble A Team

  • Systematic Reviews require more than one person. You may need content experts, statisticians, information professionals, and more.

Step 3: Develop Your Question

  • Systematic Reviews require a focused research question.There are different frameworks to help develop your question based on whether you are doing a quantitative (PICO) or qualitative (SPIDER) study.

Step 4: Determine Your Eligibility Criteria 

  • Defining what types of studies will be included in your study before you start is a critical part of a systematic review. Criteria must be specific and limit any ambiguity or loopholes. 

Step 5: Develop Your Protocol

  • A key piece of the process is the review protocol. A systematic review protocol should describe the proposed approach for the review and the details for how the review will be conducted. The protocol should: 

    • Provide background information on the topic of the review;
    • Outline the question(s) that the review will address;
    • Detail the inclusion and exclusion criteria;
    • Describe how the authors will manage the review process; and,
    • Describe the process for identifying, assessing, and summarizing studies in the review.

Step 6: Developing Your Search

  • The systematic review search is a form of data collection and requires time and content knowledge. 

Step 7: Review The Results

  • Screening your results to determine if they meet your inclusion criteria requires at least two people and typically has two phases: Phase 1 (Title/Abstract) and Phase 2 (Full-Text). We have a subscription to Covidence (contact a librarian for help) to aid you in this process. 

Step 8: Extract the Data

  • After screening is complete you will need to extract data from your identified relevant articles. We have a subscription to Covidence (contact a librarian for help) to aid you in this process. 

Step 9: Assess Selected Studies

  • You now have your final set of articles and need to assess the quality of data in them. There are numerous tools or frameworks to help during this critical appraisal process, including AMSTAR 2, ROBIS, CASP, and more

Step 10: Analyze Data

  • Analyzing the data and interpreting the results can follow either a quantitative analysis (e.g., meta-analysis), descriptive analysis (e.g., narrative synthesis), or some combination of the two. 

Step 11. Write the Review

Step 12: Update the Search

  • Systematic reviews often take years to complete and often required an updated search to be run to locate any new material. Make sure you have documented and saved your previous searches to make this process easier


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