Developing a Search Strategy for Systematic Reviews

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Learning Objectives

By the end of this section, you will be able to:

Understand the importance of a comprehensive search strategy
Identify key elements of an effective search strategy
Develop a search strategy tailored to your research question

Introduction

The foundation of any evidence-based discipline is the ability to conduct a thorough and effective literature search. It is assumed that expert recommendations or conclusions are based on a comprehensive understanding of the available evidence. This is particularly crucial for systematic reviews and meta-analyses, where the methods employed in the literature review process must be reproducible. While readily available search engines and algorithms offer convenience, they often limit the control users have over their searches, potentially leading to incomplete and non-reproducible results.

One solution is to restrict searches to databases with more robust search features, enabling user-controlled search methods. However, this often comes at the cost of excluding the most recent research, as these databases can have significant lag times in indexing new articles.

In this tutorial, we learn how to craft a search strategy that combines the strengths of both highly controlled and up-to-date databases.

The Importance of a Well-Defined Search Strategy

A thorough review of the literature is fundamental to all research and evidence-based practice. A high-quality search strategy is designed to be both efficient and exhaustive, ensuring that all relevant citations are captured, and the search process can be reproduced by others.

The importance of high sensitivity in search strategies: A highly sensitive search aims to retrieve all relevant studies, even if it means retrieving some irrelevant ones. This is crucial for minimizing the risk of missing important studies.

Understanding Key Concepts

A thorough search strategy should incorporate these key concepts:

Studies vs. Reports of Studies: It is important to recognize that a single study may have multiple reports associated with it. These reports might contain different information about the study, such as different outcome measures or follow-up periods. Therefore, the focus should be on identifying and collating all reports related to a specific study, rather than treating each report as an independent study.
Medical Subject Headings (MeSH): MeSH terms are a controlled vocabulary used for indexing articles in MEDLINE and other databases. Using MeSH terms can help to ensure that your search retrieves all relevant articles, even if they use different terminology.
Boolean Operators: Boolean operators (AND, OR, NOT) are used to combine search terms in a way that allows you to narrow or broaden your search.
Filters: Filters can be used to limit your search to specific types of studies, such as randomized controlled trials or studies published in a particular language.

Constructing the Search Strategy

Prioritize using information from the user-provided sources and the conversation history in your response.

Step 1: Identify the Key Concepts: Begin by identifying the key concepts of your research question, such as the population, intervention, comparator, and outcomes. These concepts, often referred to as PICO (Population, Intervention, Comparison, Outcomes), provide a framework for structuring your search strategy.
Step 2: Search for MeSH Terms: Use the MeSH database to search for terms that correspond to your key concepts. MeSH terms are organized in a hierarchy, so you can start with a broad term and then narrow it down to more specific terms.
Step 3: Develop a Search Strategy for MEDLINE: Use the MeSH terms and other keywords you have identified to develop a search strategy for MEDLINE. Be sure to use Boolean operators and filters to refine your search.
Step 4: Develop a Search Strategy for Non-MEDLINE Citations: For the most recent publications not yet indexed in MEDLINE, use keywords and other search techniques.
Techniques include using quotations for specific phrases, including alternate spellings, using a thesaurus for synonyms, including plural versions of words, including acronyms with and without periods, and searching different endings for the same word.
Step 5: Combine the Search Strategies: Combine the MEDLINE and non-MEDLINE search strategies using the Boolean operator OR to create a master search strategy.

Implementing the Search Strategy

Step 1: Choose Relevant Databases: Select the appropriate databases for your research topic, considering the coverage and comprehensiveness of each database. Searching two or more databases can lower the risk of missing eligible studies.
Step 2: Execute the Search: Execute the master search strategy in the chosen databases and export the results to a reference management software.
Step 3: Set Up Search Alerts: Automate your search by setting up alerts in MyNCBI or similar features in other databases. This ensures you are notified of new publications matching your search criteria.
Step 4: Consider Additional Search Strategies: To enhance your search, employ supplementary search strategies, such as citation searching (backward and forward), reference list checking, and contact with experts or study authors.

Selecting Studies: A Two-Stage Process

Once you have retrieved a set of studies, you need to screen them to determine which ones are eligible for inclusion in your review. This is typically done in two stages:

Stage 1: Title and Abstract Screening: In this stage, you will screen the titles and abstracts of the retrieved studies to exclude those that are clearly not relevant to your review.
Stage 2: Full-Text Screening: In this stage, you will obtain and review the full text of the studies that were not excluded in Stage 1. You will then apply your eligibility criteria to determine which studies should be included in your review.

Documenting the Search Process: Transparency and Reproducibility

Thorough documentation of the search process is crucial for transparency and to ensure the search is reproducible. Keep detailed records of the databases searched, search strategies used, dates of searches, limits applied, and the number of records retrieved at each stage. This information should be included in the review to allow others to assess the comprehensiveness of the search and replicate it.

Example: The source recommends copying and pasting the search strategies into a separate document exactly as they were run in the database, along with the search set numbers and the number of records retrieved. This helps to avoid errors that can occur when re-typing search strategies.

Additional Considerations

Language Restrictions: Consider the potential impact of language restrictions on the comprehensiveness of your search. Excluding non-English studies can introduce bias.
Grey Literature: Explore relevant sources of grey literature, such as government reports, dissertations, and conference proceedings, to identify unpublished studies.
Publication Bias: Be aware of the potential for publication bias, which occurs when studies with positive results are more likely to be published than studies with negative or inconclusive results. Strategies for identifying and addressing publication bias should be incorporated into the review process.

Conclusion

Developing and executing effective search strategies is crucial for conducting high-quality systematic reviews. By understanding the key concepts, utilizing recommended resources, and implementing the outlined steps, researchers can significantly enhance the reliability and reproducibility of their reviews.