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)
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.
It is important when searching for evidence that search terms are referred back to your original PICO question. The process of finding evidence follows these steps:
1. Identify terms to fit your PICO question. These keywords will be used in searching databases. 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.
2. Find systematic reviews - 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.
3. 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.
4. Search the Grey Literature, such as conference proceedings, theses, reports and unpublished literature.
5. Hand searching involves examining manually key journals, conference proceedings and other relevant publications. Hand searching 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.
6. Appraisal and selection of studies. Structured appraisal helps to select the highest quality evidence available and minimise bias.
7. 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
8. 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.
Document the search process:
The search process needs to be documented in enough detail to ensure that it can be reported correctly in the review and reproduced for verification.
For each database search record:
EndNote software can be used to record full bibliographical details for each citation and additional notes relating to the selection and evaluation of that source.
Report search results:
There are a number of places where searches can be reported. These include the appendix, the review abstract, the methods section or the results section.
Why is it important to have a plan?
A major cause of bias in a systematic review is answering a different question to that being originally asked. This is why it is important to develop a review plan or protocol.
The benefits of having a protocol before the beginning of a review:
The protocol should include:
Registering your protocol helps avoid duplication of work. You do not want anyone else to do the exact same review you are doing.
A good place to register a health review is PROSPERO. Once you register your review will:
You can publish your protocol. For example, in the Systematic Reviews journal:
Protocols for Cochrane and Joanna Briggs Institute reviews are published on their websites:
Many other journals will allow you to publish your protocol. You should also look for relevant journals within your discipline area.
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:
SPIDER can be used for both qualitative and quantitative studies:
Pl: Phenomenon of Interest
R: Research Type
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