Planning

Evidence searches for systematic reviews

for your search in support systematic reviews.

The suggested time to allocate to this search.

No maximum time, systematic reviews are large scale projects, and it is advisable to put-aside adequate time for searching, meetings and correspondence with the requester and their team.

Non-urgent advice: Communication is vital

Ask the requester their timescales and when they would like the results by.

If the suggested time scale is too short advise them of an appropriate date.

It is reasonable to explain to the requester that as systematic review searches are complex, carried out across multiple databases, registries and websites, and require extensive testing, longer delivery time scales are usual.

As a rough guide delivery time scales are commonly at least 10 days to complete the initial searches with revisions possible as the review progresses

Please read:

  • "All evidence searches" (see "Quick links") before proceeding
  • and the "Supplement" section for examples of this type of search

General points to consider

Systematic review or literature review?

Carrying out a systematic review is a highly structured activity governed by internationally recognised guidance. Requesters can mistakenly use the blanket terminology “systematic review” when they really wish to carry out a systematic search of the evidence.

If required, refer your requester to the following for definitions and descriptions on types of review

Sutton et al (2019) Meeting the review family: exploring review types and associated information retrieval requirements identifies 48 distinct review types, rapid reviews, systematic reviews, realist reviews, etc., and highlights the expansion of methodological approaches.

The Women and Newborn Health Service Library’s guide 'What is a Systematic Review and how does it differ from a Literature Review?'

For a systematic search of the evidence/literature review please follow the section in this guide on Evidence Searching to Support Research/Writing for Publication.

For a ‘true’ systematic review, this requires the gathering, collation and analysis of all the available evidence for a given research topic and is governed by the afore-mentioned internationally recognised guidance which we will come to shortly. The topic normally will be looking at some type of intervention and its effectiveness.

Due to the scale of the work a systematic review often takes a number of months, and your help and advice may be sought at different stages of the review over this period.

Review protocols

A review protocol is written prior to beginning work on the review proper. Protocols are registered on the PROSPERO database, unless the requester is writing a review for Cochrane in which case it is submitted to Cochrane and from there automatically launched onto Prospero. You should advise the requester to submit their protocol to Prospero, if they are unaware.

Internationally recognised guidance

Internationally recognised guidance governing systematic reviews - Be familiar with the following lead sources of guidance. A systematic review must follow this guidance.

Cochrane Handbook

Cochrane Handbook for Systematic Reviews of Interventions.

The handbook and its technical supplement will be updated around August of each year.

MECIR Handbook

Methodological Expectations for Cochrane Intervention Reviews (MECIR).

Supplementing the Handbook, key aspects of handbook guidance are collated in MECIR and this provides the core standards that are generally expected of Cochrane reviews. Each MECIR item includes a link to a relevant handbook chapter.

PRISMA

The 3 key elements below govern the reporting of the complete review:

PRISMA statement - a checklist for each section of the review.

PRISMA protcols - PRISMA-P guidance for writing the review protocol.

PRISMA statement flow diagram - charts the flow of information through the course of the review. Different templates are available depending on the type of review (new or updated) and sources used to identify studies.

The Cochrane Handbook and PRISMA essentially give the same instructions but complement and overlap each other. PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) provides a concise checklist and is a good place to start for those new to the process.

There is also PRISMA-S which governs how the ‘searches supporting the review’ are recorded. This is of key relevance to the information professional when recording search activity.

This additional guidance and resources may prove to useful:

Ask them to review the results:

  • Are they as expected?
  • Are further search terms to be added or removed from the strategy?

Include with your draft the definitions used in the scope notes of indexing terms for information, this can help the requester.

Remember to stress that for the search to be truly comprehensive they will see a significant number of references that are not on target. These will need to be identified and discarded as part of their sift.

Scoping searches and formulating research questions

Have they performed a scoping search and is the research question fully formulated?

If not, they may want you to undertake some scoping searches to help finalise the question, see what research has already been carried out and if a recently published review already exists on this topic.

This will give them a sense of how much research is ‘out there’, how many results they can expect to screen and will help to set timescales to manage their project.

If they have carried out some preliminary searches it is useful to see the strategies to help you understand the search topic and its scope. If they are aware of relevant published studies on the topic, ask them to send these to you to inform your search.

Is guidance needed to finalise the review question?

If yes, refer requester to Chapter 2, Determining the scope of the review and the questions it will address of the Cochrane Handbook for useful help.

Writing the protocol

If they have finalised the review question and a scoping search has been undertaken, have they written their protocol?

If yes, you need to see this as it details the inclusion and exclusion criteria for the search in addition to giving you a clearly defined research question.

If no, check they are aware of the following 4 areas of guidance which will help them write their protocol:

Is this the requester’s first systematic review?

If yes, regarding the methodology and the reporting of review findings, the PRISMA guidance is very easy to follow and is endorsed by Cochrane.

Refer new systematic reviewers to the PRISMA checklist if a quick overview of the whole process would be helpful.

Databases, resources and filters: what should I include?

This will depend on the question and subject area. A question that is clinical in nature will require biomedical databases such as Medline, Embase and CINAHL.

A topic relating to mental health will need to include databases with a mental health focus such as PsycINFO and PsycArticles.

See the Cochrane Handbook Chapter 4, section 4.3.1.1 for further guidance.

Chapter 4 of the Cochrane Handbook also states that Medline, Embase, and the Cochrane Library’s CENTRAL, are the recommended minimum for database coverage:

The Cochrane Technical supplement to chapter 4 provides concise guidance on searching and selecting studies.

To avoid publication bias it is also important to search clinical trial registries. This will help to identify trials that may have been stopped, withdrawn or the results were not published.

Search clinical trials registers for in-progress trials, including (but not limited-to):

It is usual to also perform a citation search to identify additional relevant studies. This involves searching for those studies that have been cited by relevant articles.

The relevant articles can be those which have been selected from the search results already obtained or could be from the articles identified as relevant by the researcher at the very beginning of the review.

Citation searches can be carried out using citation indexes such as:

  • Scopus (££), if available
  • Google Scholar and PubMed also permit limited citation searching via their “cited by” or “citations” links (Please note: these may refer to online publication only)

Also search preprint servers including Europe PMC.

For further resources to search the following sites may also be useful:

Consider appropriate search filters if your search is looking for a particular study design or population.

The ISSG Search Filters Resource is a vast resource of published search filters designed to retrieve research by study design or focus.

If you include a search filter, you must report your decision to do so in your search methods.

Develop a search strategy as part of your planning:

It may be useful to draft a search strategy on Medline initially and send this to the reviewer along with a sample of the results, such as the first 50 references.