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Systematic Review Guide

Planning for a systematic review is crucial to ensure the research is relevant, rigorous and replicable.

It begins with checking for similar or ongoing studies to avoid duplication, followed by formulating a clear, focused research question and gathering example articles. Writing and registering a protocol before starting formal work provides transparency, helps prevent bias and guides all team work that will be invested into the review.

Searching for existing protocols and evidence during the planning stage of a systematic review means checking whether similar reviews or protocols already exist in databases such as PROSPERO, Cochrane Library, and PubMed.

Why is it important to search for existing studies and protocols?

  • Avoids duplicating research.
  • Determines if there is enough evidence for you to synthesise in a review.

If the research question has already been answered or is underway, you may consider updating a dated review or amending your question.

How do you search for existing studies and protocols?

Example
Connor, a clinical psychologist, plans to conduct a systematic review on mindfulness-based interventions for reducing anxiety in adolescents. Before starting, he searches PROSPERO and finds an existing registered protocol examining mindfulness for anxiety in adolescents with chronic illness.
Realising his initial topic overlaps, he reviews the existing protocol’s scope and decides to amend his research question to focus instead on school-based mindfulness programmes for general adolescent populations.
This adjustment allows her review to fill a distinct evidence gap, avoid duplication, and contribute new insights to the field.

Recommended resources:

Literature Searching Guide

A good question is the first step in any review. Your systematic review must be based on a research question that:

  1. Is focused and answerable
  2. Adds new research on a topic
  3. Considers the right study designs

Why is it important to have an appropriate research question?

  • Defines scope, inclusion/exclusion criteria, and search strategy.
  • Fcuses the review on a meaningful and answerable issue.
  • Makes objectives and findings easier to interpret.

How do I create an appropriate research question?

  1. Review existing literature and protocols (e.g. PROSPERO) to find areas where new evidence is needed.
  2. Define the main elements
    1. Use frameworks like PICO (Population, Intervention, Comparator, Outcome) for quantitative reviews or PEO/PECO for qualitative/mixed-methods.
  3. Ensure focus and specificity
    1. Make the question clear, narrow enough to be answerable, but broad enough to capture relevant studies.
  4. Select appropriate study designs
    1. Choose designs that can answer the question (e.g., RCTs for interventions, cohort studies for prognosis, qualitative studies for experiences).
  5. Ensure sufficient studies exist, and that outcomes and populations are measurable and reported.
  6. Pilot your question by searching a few databases to see if it retrieves relevant studies. Adjust wording if too broad or too narrow.
  7. Document the final question
Example
Jamie, a physiotherapist, wants to explore ways to improve patient recovery after hip replacement surgery. They identify a gap in the literature regarding the effectiveness of progressive resistance exercise programmes in the first six months post-surgery.

Using the PICO framework, they define their population as adults post-hip replacement, the intervention as a structured progressive resistance exercise programme, the comparator as standard physiotherapy, and the outcomes as mobility, pain, and quality of life.
They decide to include RCTs and quasi-experimental trials, check that enough relevant studies exist, and tests search keywords in MEDLINE to ensure they retrieve appropriate studies.

Finally, they document the refined, focused research question and rationale in their systematic review protocol.

Recommended resources:

Literature Searching Guide: Develop Question

Inclusion and exclusion criteria in a systematic review are the predefined rules used to determine which studies will be considered relevant for the review. Inclusion criteria specify the characteristics that studies must have to be included, while exclusion criteria identify characteristics that disqualify studies.

Why is it important to have clear inclusion and exclusion criteria?

  • Ensures all reviewers apply the same rules when screening studies.
  • Prevents arbitrary or subjective decisions.
  • Keeps the review aligned with the research question.
  • Allows others to understand and replicate study selection.

How do I determine the inclusion and exclusion criteria?

The criteria is determined after developing the research question and before the final search is conducted. It should be informed by test literature searches and background research.

Common inclusion/exclusion criteria:

Criteria Examples of inclusion/exclusion criteria
Date Limit to most recent 10 years
Patient group Child, Adult, Older adults only, a condition group
Study designs RCTs or observational studies only
Language English language only
Publication type Primary research, only peer reviewed studies, news and opinion
Setting Acute, primary or secondary care
Location Geography, developing or developed countries
Other Confounding factors that would skew or negate the results

Recommended resources:

Elsevier Health Education. (2022). Virtual Tutor, Research Series: Session 4; Inclusion and Exclusion Criteria.

A gold set in a systematic review is a predefined set of studies that are known to be relevant and meet the inclusion criteria. It is often used to test, validate, or calibrate the search strategy and screening process.

Why is it important to have a gold set?

  • A gold set can validate the search strategy by ensuring it can identify known relevant studies.
  • Helps reviewers apply inclusion/exclusion criteria consistently.

How do I find and use a gold set?

  1. Select a small number of studies that are definitely relevant to your review question. These can come from prior knowledge, expert recommendations, or preliminary searches.
  2. Incorporate the keywords and subject headings from your gold set in your database searches
  3. Run your database search and confirm that all gold set studies are retrieved.
    1. Adjust search terms, Boolean operators, or filters if any are missed.
  4. Have reviewers screen the gold set to practice applying inclusion/exclusion criteria consistently.
  5. Record which studies are included, why they were chosen, and how they were used in testing and calibration.
  6. Repeat if necessary
    1. After refining the search or screening process, re-test with the gold set to ensure improvements have captured all key studies.
Example
Dr. Lee, a clinical researcher studying interventions for post-stroke rehabilitation, creates a gold set of five well-known, highly cited trials that clearly meet her inclusion criteria.
She runs her initial database search and checks that all gold set studies are retrieved; when one study is missed, she refines her search terms and filters. She then has her team practise screening the gold set to ensure consistent application of the inclusion and exclusion criteria.
By documenting the gold set and how it was used to test and calibrate both the search strategy and screening process, Dr. Lee increases confidence that her systematic review will capture all relevant studies.

A protocol in a systematic review is a detailed plan that outlines the objectives, methods, and procedures of the review before it is conducted. It specifies the research question, eligibility criteria, search strategy, data extraction, risk of bias assessment, and synthesis approach.

Why is it important to have a protocol?

  • Ensures transparency by clearly documenting the methods before starting the review.
  • Prevents post hoc changes to inclusion criteria or analyses.
  • Supports planning and organisation – guides search strategy, screening, and data extraction.
  • Enhances the review's credibility by demonstrating methodological rigour.

How do I write a protocol?

The protocol document must include:

  • Description of a clear and answerable research question that will be investigated
  • The inclusion and exclusion criteria for selecting studies
  • Eligibility criteria for potential studies 
  • A search strategy from at least one database that will be translated to other databases and is reproducible
  • Critical appraisal and/or quality assessment tools that will be used
  • Information about how bias will be assessed
  • Extraction tools and guidelines that will be followed

 

Templates for system review protocols are available online:

How do I register my protocol?

Protocols must be made publicly available in a registry such as those listed below, prior to commencing a systematic review. Journals will require registered protocols to consider systematic review manuscripts.

 

Some journals also publish systematic review protocols. To determine the best approach, check instructions to authors provided by the journal/s you plan to publish with. They may have directions about protocol registration.

The following journals publish systematic review protocols:

Example
Phuong, H., et al. (2024). Outcomes of collective leadership models within the healthcare setting: a systematic review. PROSPERO 2024 CRD42024568395.

Recommended resources:

Dutta, D. (2025). Steps to register a protocol for systematic review at PROSPERO (Dr Deep Dutta Endocrinologist).