Evidence Synthesis Methodologies in the Health Sciences

What is exploratory searching?

All systematic searches begin with exploratory searches. Exploratory searching helps you:

• Learn the scope of existing literature.
• Locate seed articles.
• Select relevant databases.
• Identify potential search terms.
• Test how different terms impact results.

How do I get started with exploratory searching?

The main ideas in your research question and any relevant articles you've already identified will both be helpful in these initial explorations. Some useful strategies include:

• Breaking your research question into its most important ideas.
• Brainstorming terms for each main idea based on your existing knowledge.
• Harvesting language used in the titles and abstracts of relevant articles.
• Running simple searches in PubMed and other potentially useful databases.
  • Harvesting terms from their titles, abstracts, and author keywords.
  • Noting the controlled vocabulary terms assigned to relevant articles.
• Reviewing other evidence syntheses on your topic.
  • Reading their methods to find terms they used in their searches.
  • Tracking down their supplementary materials to see full search strategies.
• Looking at the references of relevant articles.
• Tracking down articles that have cited highly relevant articles since their publication.
• Searching the controlled vocabulary in PubMed and other databases to see how your ideas are described.

How should I keep track of my searches in the exploratory phase?

Documenting your exploratory process, such as in a concept table and/or a search diary, is an efficient way to keep track of useful information and avoid duplicating work. A search diary can be as simple as a running Google Doc with dates and some notes about where and what you searched. Learn more about concept tables below.

How does that differ from keeping track of my final searches?

Much more thorough documentation is required during the reporting phase of your project. A concept table or search diary is useful at the exploratory stage, but insufficient for final reporting.

As you prepare and execute your final searches, remember that reporting guidelines will typically require that you document:

• Every method you used to identify references to screen, including specific search tools (such as databases, search engines, and websites) and other approaches (citation searching, websites, grey literature, etc.).
• The exact final search strategies you used for every database or other searching tool.
• How many references you found in each database and via other search methods.
• The number of deduplicated refences, how many you retained at each stage of screening, and other details of the screening process.

This is covered in more detail on the Download and Manage Results, Document Your Searches, and Report Results pages of this guide.

When crafting a complex search strategy, a concept table can help you focus on the main ideas in your research question and gather terminology to use in your search.

This tutorial, Developing Your Systematic Search Strategy Using a Concept Table, walks you through the process of using the concept table to generate and document search terms.

Click the image (or the link below it) to open the tutorial in a new window. You will be asked to register if you do not yet have a Reach 360 account.

The templates below, for concept tables in Docs or Sheets format, can be copied into your Google Drive.

Seed articles, sometimes called sentinel or benchmark articles, typically address your research question and meet the inclusion criteria for your project. A set of seed articles may also include things like literature reviews and evidence syntheses closely related to your research question, articles cited in those reviews, relevant references from your seed articles, or articles citing your seed articles.

Seed articles can be used to:

• Identify controlled vocabulary and free text terms.
• Locate existing systematic search strategies that have been used for concepts in your research question.

They can also be used to test your searches for thoroughness. Create a search that includes just your seed articles. Then run your systematic search. Finally, use a Boolean OR to combine the two sets. If the number of results matches your systematic search, it's a good indication you've created a thorough search. If the articles do not appear, look at the missing seed articles in the database to see what elements may be missing in your search strategy.

Inclusive language and equity considerations

Population research requires thorough research into how groups are described in current and past scholarly and clinical literature, as well as how they have described or currently describe themselves. Research into health equity requires some special considerations, and resources exist to guide this work.

Problematic and outdated language

Language used to describe complex population topics such as race, ethnicity, and gender has evolved over time, and continues to evolve. In designing comprehensive systematic searches, it's often necessary to include outdated terminology for free text terms. Even controlled vocabulary may be outdated; even if it has been revised, sometimes the database has replaced previous indexing applied to older articles. This can be frustrating and even deeply uncomfortable. The article linked here provides some guidance for how to handle this issue.

Search hedges or filters

A search hedge, sometimes called a search filter, is a single concept systematic search strategy created by an expert searcher. Hedges are most frequently designed to facilitate searches for frequently searched concepts such as study designs, population groups, or specific topics. They may be formally validated, but at minimum have been tested to some degree for effective performance.

Because they are designed by experts to be as comprehensive as possible, hedges are preferable to the built-in filters seen in many databases (e.g., using a publication type limit in PubMed) when performing systematic searches.

Hedges are typically designed for a single database, such as APA PsycInfo, and for a specific platform, such as EBSCOhost. They incorporate both the database's controlled vocabulary (if any) and the unique syntax of the platform.

While locating hedges can be challenging, some reliable sources are listed below.

Other existing searches

Evidence syntheses on topics related to your own research question should provide their search strategies. Examining these may help you design your own search. In most cases, the full search strategies, if available, will be in the supplementary materials. They may also be posted in institutional repositories or in other types of repositories, such as searchRxiv.

Ethical use of hedges, filters, or other existing search strategies

Citing sources is essential when using others' search strategies. Be sure to fully credit any searches that informed your own, whether you used the search as written or adapted it.