An Introduction to Evidence Synthesis Searching

The search for sources of evidence is a fundamental component of all the diverse types and methodologies of systematic and scoping reviews (Munn et al. 2018). Searches must be as comprehensive as possible while recognising that there are limitations to this goal. Searches must be explicit, transparent and reproducible. Readers and users of systematic and scoping reviews must be able to readily identify which steps were taken in the search, including which databases, versions of databases, platforms and resources were searched and when, and which keywords, controlled vocabulary, field tags and limits were used. If search filters (sometimes called search blocks, hedges or strings) are used, these must be cited. Moreover, while not required, it is courtesy to indicate who conducted the search (Ross-White 2021). This information is presented in the manuscript, generally as an appendix.

It is difficult to prescribe a particular search methodology, as review questions and resources vary considerably. As an example, while a question relating to the behavioural aspect of illness would require a search in the PsycINFO database, questions that do not relate to behaviour or psychology might not need a search in that database. While PubMed provides free access to MEDLINE, searching MEDLINE on the Ovid platform provides greater functionality for controlling the search process through more sophisticated proximity searching (e.g. ADJn). Many institutions have different subscriptions to databases that are similar in content, so this access to resources may determine which databases are searched. JBI has endorsed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) standards for reporting protocols and reviews, including searches (Moher et al. 2009; Page et al. 2021). Familiarising yourself with the PRISMA, PRISMA-S, PRISMA-ScR and PRISMA-P requirements as well as any relevant PRISMA extensions for reporting at the outset of a review ensures that the necessary documentation will be followed.

The JBI 3-Step Search Process

What differentiates JBI reviews in the search component is our explicit 3-step search process.

The first step is an initial exploratory search (usually of MEDLINE and CINAHL databases) to find ‘seed references’ –– that is, records of studies that meet the inclusion criteria for the review question. Google, Google Scholar, Library discovery tools (PRIMO, OneSearch, SumSearch, etc.) and Generative AI tools (e.g. ChatGPT) can be useful for finding these seed references. However, for sources found via ChatGPT, it is important to verify that they are not hallucinations. Following these initial exploratory searches, the keywords in the title and abstract, along with indexed terms (also referred to as MeSH terms, Thesaurus, Controlled Vocabulary) of the seed references are harvested. Consultation with the review team to gather other keywords and indexed terms should be sought.

The second step is to develop a comprehensive search strategy using these harvested keywords and indexed terms for the key database for the protocol. The development of a comprehensive search is an iterative process that involves testing combinations of keywords and indexed terms and checking that the seed references are being captured by the search strategy. Once the search strategy is developed in the primary database, it is then translated across to other databases and grey literature sources. Some databases, such as Embase, CINAHL and PsycINFO, include grey literature.