A systematic review aims to comprehensively identify and synthesize all relevant evidence on a specific research question. A well-developed search strategy is crucial to ensure that all relevant studies are included in the review, minimizing bias and ensuring the inclusion of all relevant evidence. This guide outlines the process of developing a comprehensive list of keywords and synonyms to use in crafting search strategies for systematic reviews.
Defining the Research Question
Before starting the keyword search, it is essential to define the research question clearly. A well-defined question helps focus the search and identify the key concepts that need to be included in the search strategy1. Frameworks like PICO (Population, Intervention, Comparison, Outcome) can be helpful in defining the research question and identifying the key concepts1.
It's also important to decide where to search. This involves selecting the appropriate databases that cover the relevant literature for the research question3. For example, in clinical medicine, common databases include MEDLINE, Embase, and CENTRAL3. Depending on the subject of the review, it might also be necessary to search in databases that cover specific geographical regions or specialist areas.
Identifying Keywords and Synonyms
Once the research question is defined and the databases are selected, the next step is to identify keywords and synonyms related to each concept. This involves brainstorming and consulting various resources to ensure that all relevant terms are included4.
Brainstorming
Start by brainstorming keywords and phrases that describe each concept in the research question. Consider different ways to express the same concept, including variations in terminology, spelling, and abbreviations4. For example, if one concept is "heart attack," consider including synonyms like "myocardial infarction," "cardiac arrest," and "coronary thrombosis." 5
To better organize the keywords and synonyms, it can be helpful to use a table format:
Concept
Keywords
Synonyms
Heart Attack
heart attack
myocardial infarction, cardiac arrest, coronary thrombosis
Depression
depression
depressive disorder, major depressive disorder, clinical depression
Consulting Resources
Several resources can help identify keywords and synonyms:
- Thesauri and Dictionaries: Use thesauri (like Thesaurus.com 6) and dictionaries to find synonyms and related terms for each concept.
- Subject Heading Lists: Many databases, such as MEDLINE and Embase, use controlled vocabularies or thesauri (like MeSH) to index articles7. These lists can be valuable resources for identifying relevant keywords and synonyms1. When using a database with a controlled vocabulary, map each concept to the relevant terms in that vocabulary8.
- Existing Reviews: Examine similar systematic reviews to identify keywords and synonyms used in their search strategies9.
- Experts: Consult with experts in the field to get their input on relevant terminology and search terms.
- Librarians: Collaborating with a librarian can be invaluable for generating keywords and mapping concepts to a controlled vocabulary10. They have expertise in search strategies and can provide guidance on using databases and resources effectively.
When identifying synonyms, it's important to think laterally and consider how others might describe the same concept9. This includes considering international terminology, spelling variations (e.g., "behaviour" in British English vs. "behavior" in American English), colloquialisms, and related terms.
Types of Keywords
Consider different types of keywords to ensure a comprehensive search:
- Free Text Terms: These are words and phrases that appear in the title, abstract, or full text of an article11. They are essential for capturing articles that may not be indexed with specific subject headings5. Free text searching generally has high recall (finds many articles) but low precision (many irrelevant results)12.
- Controlled Vocabulary Terms: These are standardized terms used by databases to index articles3. Using controlled vocabulary terms can help retrieve more relevant results3. Controlled vocabulary searches have lower recall but higher precision12.
It's important to use a combination of both controlled vocabulary and free text terms to construct a highly sensitive search strategy7. This ensures that the search captures as many relevant articles as possible.
To further refine the search, consider limiting searches by field (e.g., title, abstract)11. This can help improve the relevancy of the results by focusing on specific areas where the keywords are likely to appear.
Using Tools and Resources
Several tools and resources can help identify keywords and synonyms:
- Text Mining Tools: These tools analyze text to identify frequently occurring words and phrases, which can be used as keywords13. Examples include WordFreq, PubMed PubReMiner, and TerMine.
- Keyword Research Tools: Tools like Moz Keyword Explorer, Google Keyword Planner, and Semrush can help identify relevant keywords and synonyms14.
- Online Resources: Websites like ReadWriteThink and TeachStarter provide resources for identifying synonyms17.
Analyzing Website Data
If the systematic review is related to a website or online content, Google Search Console can be a valuable tool for identifying declining keywords that need attention19. By analyzing website data, researchers can identify terms that are losing traffic and may need to be updated or expanded in the search strategy.
Combining Keywords and Synonyms
Once a comprehensive list of keywords and synonyms is developed, use Boolean operators to combine them effectively in the search strategy20.
- OR: Use OR to combine synonyms and related terms. This broadens the search and ensures that articles using different terms for the same concept are retrieved20. For example, "depression OR depressive disorder."
- AND: Use AND to combine different concepts. This narrows the search and ensures that only articles containing all the specified concepts are retrieved20. For example, "depression AND anxiety."
- NOT: Use NOT to exclude specific terms from the search. This can be helpful for eliminating irrelevant results20. However, use NOT cautiously as it may exclude relevant articles.
To illustrate the combination of synonyms and concepts using Boolean operators, consider this example: "(depression OR depressive disorder) AND (therapy OR treatment)." This search strategy would retrieve articles that discuss either depression or depressive disorder and include information on either therapy or treatment.
Refining the Search Strategy
After creating the initial search strategy, it's crucial to refine it to ensure that it retrieves relevant results. This involves:
- Testing the Search: Run the search strategy in the chosen databases and examine the results21.
- Analyzing the Results: Identify any irrelevant results and adjust the search strategy accordingly4. This may involve adding more keywords, using different Boolean operators, or limiting the search by field.
- Iterative Process: Repeat the testing and analysis process until the search strategy retrieves a satisfactory set of results.
During the refining process, it's important to be aware of the trade-off between precision and sensitivity3. Favoring sensitivity (capturing more potentially relevant records) is generally preferred in systematic reviews to ensure comprehensiveness, even if it means retrieving some irrelevant records.
Citation Chasing
Citation chasing is a technique that can be used to identify additional relevant articles8. This involves examining the reference lists of known relevant articles to find other potentially relevant studies. It can also involve searching for articles that have cited the known relevant articles.
Conclusion
Developing a comprehensive list of keywords and synonyms is crucial for crafting effective search strategies for systematic reviews. By following the steps outlined in this guide and utilizing the available tools and resources, researchers can ensure that their searches are comprehensive and retrieve all relevant evidence to answer their research question. This meticulous approach to keyword generation is essential to minimize bias and ensure the inclusion of all relevant evidence, ultimately contributing to the rigor and validity of the systematic review.
Works cited
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