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Systematic Reviews: Systematic review process

A guide to assist staff and students undertaking systematic reviews

Developing a systematic Review

Systematic review process

  • Identify any recent or ongoing systematic reviews.
  • Formulate the question - a clearly defined question will ensure that your research produces relevant results.
  • Write the protocol, which includes the inclusion/exclusion and eligibility criteria. The protocol defines the process for selecting studies and reduces the risk of bias.
  • Register your protocol
  • Develop the search strategy.
  • Search relevant sources to identify the evidence.
  • Appraise and select suitable studies.
  • Synthesise the data.
  • Document and report the search strategy.

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. It's always necessary to check whether a systematic review answering your question has already been conducted or is under way. Published reviews also provide a starting point for identifying the studies.

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. Identify terms to fit your PICO question. These keywords will be used in searching databases. Find journal articles - search for published primary studies in databases such as MEDLINE, CINAHL, PsycINFO. Citation searching in Scopus or Web of Science, allows you to follow a research trail forwards, backwards or to related research. Check thesaurus terms in the relevant databases to identify other relevant keywords or subject terms to include in your search. Be aware of differences in American and English spelling and terminology. Thesaurus terms may also vary between databases.

5. Search the Grey Literature,  such as conference proceedings, theses, reports and unpublished literature.

6. Handsearching involves examining manually key journals, conference proceedings and other relevant publications. Handsearching is to overcome deficiencies in indexing or database coverage. The citation databases, Web of Science and SCOPUS are useful for identifying key journals and authors, as well as tracking research and citation searching.

7. Appraisal and selection of studies. Structured appraisal helps to select the highest quality evidence available and minimise bias.  

8. Synthesis of study results. Data from each individual study needs to be collated, combined and summarised. Quantitative systematic reviews use formal statisitical techniques such as meta-analysis to perform this step.

"As well as drawing results together, synthesis should consider the strength of evidence, explore whether any observed effects are consistent across studies, and investigate possible reasons for any inconsistencies" (Centre for Reviews and Dissemination, 2009, section 1.3.5). Systematic reviews: CRD's guidance for undertaking reviews in health care  

9. Document the search process.

10. Report on all steps of the systematic review process and present results. See PRISMA for further information. Links to reporting guidelines for systematic reviews (PRISMA) and other study types are available on the Equator Network website.

Formulating the question

The systematic review question is formulated a and tested during the scoping phase. There are many mnemonics available to assist you to formulate a search strategy based on the type of review you are undertaking and the kind of question you are asking.
A standard formula for structuring the review question is PICO(S) for quantitative questions and SPIDER for qualitative questions.

These mnemonics can be used to construct your research question and break down your search strategy. Remember that equal emphasis may not be put on each part of the mnemonic, and will largely depend on the topic of your systematic review.

The PICO structure can be used to help you put together a search strategy and formulate the question:

      Participants, Patient or Population       

      Intervention(s) (therapy, treatment, etc.)

      Comparison (other intervention or treatment, no treatment, etc. It's not always necessary to have a comparison group)

      Outcome(s)

      Study design (consider which study design will best answer the question)

In some cases the review question may also include the Study Design (PICOS). This is outlined in the Centre for Reviews and Dissemination, University of York, guide “Systematic reviews: CRD's guidance for undertaking reviews in health care”:

“The review question can be framed in terms of the population, intervention(s), comparator(s) and outcomes of the studies that will be included in the review. These elements of the review question, together with study design, will then be refined in order to determine the specific inclusion criteria that will be used when selecting studies for the review.”

"Not every review question will specify type of study design to be included". See Levels of Evidence page for hierarchy of study design

PICo

P:    Population or Problem of interest
I
:     Interest (The phenomena of Interest relates to a defined event, activity, experience or process)
Co
:  Context (Context is the setting or distinct characteristics. Note: Context not comparator)
 

Two other mnemonics may also be used to create protocols for both qualitative and quantitative studies - SPICE and SPIDER

SPICE: Within social sciences research, SPICE may be more appropriate for formulating research questions:

S:  Setting
P:  Perspective
I:   Intervention
C:  Comparison
E:  Evaluation

 

SPIDER can be used for both qualitative and quantitative studies:

S:   Sample
Pl:  Phenomenon of Interest
D:   Design
E:   Evaluation
R:   Research Type

References

References:

Booth, A. (2006). Clear and present questions: Formulating questions for evidence based practice. Library Hi Tech, 24(3), 355-368. doi:10.1108/07378830610692127

Cooke, A., Smith, D., & Booth, A. (2012). Beyond PICO: The SPIDER tool for qualitative evidence synthesis. Qualitative Health Research, 22(10), 1435-1443. doi:10.1177/1049732312452938

Methley, A., Campbell, S., Chew-Graham, C., McNally, R., & Cheraghi-Sohi, S. (2014). PICO, PICOS and SPIDER: A comparison study of specificity and sensitivity in three search tools for qualitative systematic reviews. BMC Health Services Research, 14(1), 579. doi:10.1186/s12913-014-0579-0

Systematic review visualized

What authors do by Jessica Kaufman, Cochrane Consumers & Communication review Group /CC BY-SA 4.0