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Systematic Reviews in the Health Sciences

What is a systematic review?

A systematic review is a review of a clearly formulated question that uses systematic and reproducible methods to identify, select and critically appraise all relevant research, and to collect and analyse data from the studies that are included in the review.

A systematic review:

  • Answers a focused research question
  • Employs a comprehensive, reproducible search strategy
  • Identifies ALL relevant studies (both published and unpublished)                                                         
  • Assesses all results for inclusion/exclusion, and for quality
  • Presents an unbiased, balanced summary of findings
  • Involves a team of researchers looking at a complex research question
  • Can take months, or even years, to complete. 

A systematic review can be either quantitative or qualitative.

  • A quantitative systematic review will include studies that have numerical data.
  • A qualitative systematic review derives data from observation, interviews, or verbal interactions and focuses on the meanings and interpretations of the participants. It will include focus groups, interviews, observations and diaries. For further information see our guide on Finding Qualitative Research in the Health Sciences. 

Steps in a systematic review

A systematic review involves the following steps:  

  1. Check for existing reviews/protocols. If a systematic review answering your question has been conducted, or is being undertaken, you may need to amend or refine your question
  2. Formulate a specific research question that is clear and focused. Use the PICO tool (for quantitative reviews) or PICo (for qualitative reviews)
  3. Develop and register your protocol, including the rationale for the review, and eligibility criteria
  4. Design a robust search strategy that is explicit and reproducible
  5. Conduct a comprehensive search of  the literature by searching the relevant databases and other sources  
  6. Select and critically appraise the quality of included studies
  7. Extract relevant data from individual studies and use established methods to synthesise the data
  8. Interpret your results and prepare a comprehensive report on all aspects of your systematic review. Present your findings so that they can be translated into clinical practice.

Comparison of different types of reviews

This table outlines the differences between a systematic review and a literature review:

  Systematic Review Literature Review
Question Focused on a single question Not necessarily focused on a single question, but may describe an overview
Protocol Includes a peer review protocol or plan No protocol is included
Background Provides summaries of the available literature on a topic Provides summaries of the available literature on a topic
Objectives Clear objectives are identified Objectives may or may not be identified
Inclusion/exclusion criteria Criteria is stated before review is conducted Criteria is not specified
Search strategy Comprehensive search conducted in a systematic way Strategy not explicitly stated
Process of selecting articles Process usually clear and explicit Not described in a literature review
Process of evaluating articles Comprehensive evaluation of study quality Evaluation of study quality may or may not be included
Results and data synthesis Clear summaries based on high quality evidence Summary based on studies where the quality of the articles may not be specified. May also be influenced by the reviewer's theories, needs and beliefs
Discussion Written by an expert or group of experts with a detailed and well grounded knowledge of the issues Written by an expert or group of experts with a well grounded knowledge of the issues

Adapted from: University of Newcastle Australia Library

  Systematic Review Scoping Review
What is it? Attempts to identify, appraise and synthesize all empirical evidence that meets pre-specified eligibility criteria to answer a given research question  A rapid gathering of literature in a given area, aiming to provide an overview of the type, extent and quantity of research available
Why choose this method? To address a clearly focused review question by finding the best available, relevant studies and synthesizing the results  To capture the breadth of literature; identify gaps in a research area; occasionally used as a precursor to a systematic review 
Question Focused research question with narrow parameters The research question is often broad
Eligibility criteria Inclusion/exclusion usually defined at outset Inclusion/exclusion can be developed post hoc
Appraisal Rigorous critical appraisal and evaluation of study quality Appraisal can be variable; typically not done, or may be done in a narrative form
Synthesis Clear summaries of studies based on high quality evidence. May include a met-analysis  The summary is usually descriptive 
Inferences Evidence based Evidence based

Adapted from: University of South Australia

A useful article:

Munn, Z., Peters, M. D. J., Stern, C., Tufanaru, C., McArthur, A., & Aromataris, E. (2018). Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. BMC Medical Research Methodology, 18(1), 143. https://doi.org/10.1186/s12874-018-0611-x

"Rapid reviews have emerged as a streamlined approach to synthesizing evidence-typically for informing emergent decisions faced by decision makers in health care setting".  

  Systematic Review Rapid Review
Question Often a focused clinical question (focused PICOS) Narrow question (may use PICOS)
Sources and searches Comprehensive sources searched and explicit strategies Sources may be limited but sources and strategies made explicit
Selection Criterion-based Criterion-based; uniformly applied
Appraisal Rigorous; critical appraisal Rigorous, critical appraisal (SRs only)
Synthesis Qualitative summary with/without meta-analysis Descriptive summary/categorisation of data
Inferences Evidence-based

Limited/cautious interpretation of findings

Source: Khangura, S., Konyu, K., Cushman, R., Grimshaw, J. & Moher, D. (2012). Evidence summaries: the evolution of a rapid review approach. Sytematic Review, 1-10. https://doi.org/10.1186/2046-4053-1-10

Examples of different types of reviews:

Systematic review:
Barriers and facilitators to health screening in men: A systematic review
https://doi.org/10.1016/j.socscimed.2016.07.023

Literature review:
A Literature review of mentorship programs in academic nursing
https://doi.org/10.1016/j.profnurs.2017.02.007

Scoping review: 
How do patients experiecne caring? Scoping review
https://doi.org/10.1016/j.pec.2017.03.029

Rapid review: 
Blended foods for tube-fed children: a safe and realistic option? A rapid review of the evidence
https://doi.org/10.1136/archdischild-2016-311030