What is a Search Strategy?
The search strategy guides each source you select, and the exact method used to search it. Typical sources include:
- Databases: Search of bibliographic databases such as Medline, Embase, CINAHL
- Hand-Searching: checking reference and citation lists of important papers, manual searching of a key journal's catalogue, contacting key authors for unpublished material.
- (OPTIONAL) Grey Literature: Search of grey literature, e.g. report databases, government and organisation websites, google searches
The search strategy is derived from the research question. If you have used PICO or PS to build your research question, those concepts form the basis of your search strategy.
If you would like some more training on searching (particularly in health databases!), we recommend enrolling in the following Library module in Canvas: Advanced Literature Searching for Health.
Building the Database Search from the Research Question
Use the research question to build the review's search strategy by breaking down your question into key concepts. These are usually the nouns of your sentence, and do not include relational words such as "effect", "impact", "barriers" and so on.
You may also find it simpler to adopt the PICO or PS structure if your question is about a treatment or an intervention.
We recommend developing your database search in one database first, before moving on. If you are from the health field, start with Medline (a very popular health database).
In this first search, the groundwork for the other database searches is completed by exhaustively identifying additional terms and filters. The process for the first search has four steps:
- Creating the concept table
- Identifying synonyms and subject headings
- Converting the table into the database using Boolean operators
- Adding filters to refine the search results
Steps 2-4 are repeated for other databases in a later stage of the review called "Search Translation."
Step 1: Create a concept table
To create an unbiased and thorough search, an exhaustive list of keywords and subject headings must be added. Create a concept table or matrix (perhaps in Excel or Word) to collect these additional terms. The table will look something like this at first.
P |
I |
C |
O |
|---|---|---|---|
| school children | hand washing | hand sanitiser | common cold |
Step 2: Identify keywords and subject headings
In all health databases, you can search in two ways - by using keywords or by using subject headings. A comprehensive search strategy will use both to ensure you are not missing any evidence.
Click on the tabs below to see the definitions and differences. Once you've found keywords and subject headings, add them to the table.
Keywords are terms or phrases which appear in your target articles and describe your concept.
When you enter a term, the database brings back all articles which contain that term in the record.
This means you only get what you ask for - for example if you type in 'observation' the database will only bring back articles which mention 'observation'; it won't know that you are also interested in articles which mention 'monitoring'.
As you are aiming to find ALL evidence on your topic, this means you need to think about synonyms (also known as alternative terms) for your concepts.
To come up with a shortlist of synonyms to use for each of your concepts, run some preliminary searches in PubMed or Google Scholar to see the terminology used in different articles.
Subject Headings are standardised labels the database applies to articles to group them by topic. Searching using a subject heading means you are searching by topic.
Most health databases will have a way of suggesting subject headings to you when you type in your terms - however, you can also locate them in advance.
The video below shows you how Medical Subject Headings (MeSH) works. MeSH are thesaurus of subject headings used in Medline and PubMed.
- MeSH Browser The MeSH Browser is used to explore appropriate MeSH Terms to include in your search.
P |
I |
C |
O |
|---|---|---|---|
| school children | hand washing | hand sanitiser | common cold |
| Keywords | |||
| child* | hand wash* | hand sanitizer | cold |
| adolescent* | washing with soap | antibacterial gel | viral infection |
| alcohol gel |
|
||
| Subject Headings | |||
| Child |
Hand Disinfection |
Common Cold | |
Tips
Each database has its own subject headings
Use Medline or Embase for your first search. You'll change the subject headings for every database you use.
Each database has its own syntax
Have a look at this syntax guide to learn about all the searching shortcuts available in databases like truncation (*) and adjacency searching.
- Syntax GuideAn overview of all the searching shortcuts you can use
P |
S |
|
| nurses | caring for people with diabetes | |
| Keywords | ||
| nursing staff | caregiving | diabetic patients |
| nurs* | care | diabetes |
| Subject Headings | ||
| nurses | patient care | diabetes mellitus |
| nursing care | ||
Step 3: Use Boolean operators
This step can be a bit daunting for first time reviewers, as it relies on a technical understanding of information science. Once we have all our keywords and subject headings identified, we must convert the concept table into a language the database will understand. We do this using Boolean operators.
Watch the video below to learn more about Boolean operators.
Here's a quick summary of how you should combine your terms in a PICO table.
Step 4: Add Filters
Filters (also known as limits) help focus your results. They are available in all health databases and they allow you to narrow your results using specific parameters.
Filters are very useful tools to help limit your results, however, you should only apply filters sparingly. It is very easy to apply too many and end up with zero results. Common filters to include are:
- Language e.g. English
- Publication date e.g. last 10 years, 2011-current
Tips
Some health databases will have a type of filter available called "Clinical Queries" - these are pre-made search filters that help locate a range of study types and evidence that can best answer a category of clinical question.
Examples of clinical question categories include: therapy, prognosis, diagnosis, or qualitative.
Chapter Summary
✅ Learnings
- The search strategy is an overarching framework that guides sources and searching methods, based on PICO, PS or other mnemonics.
- It is recommended to use Medline or Embase to build the search strategy, before translating it to other databases.
- There are four steps to building a search strategy:
- Creating the concept table
- Identifying synonyms and subject headings
- Converting the table into the database using boolean operators
- Adding filters to refine the search results
⚠️ I'm stuck!
I do not understand this part at all!
There's a lot of information science happening here and it takes time to get used to it. If you're totally lost, we recommend the book Doing a systematic review: A student's guide or Searching skills toolkit: Finding the evidence.
Where can I find synonyms?
You can use 'scoping searches' to find synonyms, or look at papers you've already found that match your review.
How do I find subject headings?
Databases like Medline, Embase, CINAHL and PsycINFO have mapping tools built into their database search to help you find subject headings. If you google "Find [Database Name] subject headings", you'll find instructions and videos for each one.
I can't do the Boolean part.
Boolean logic is the most challenging part of the search strategy process. First, watch this Medline video to see if it helps:
Medline Advanced Searching (UTS Library)
Need a full walkthrough? Try these resources:
Basic explanation in Searching skills toolkit: Finding the evidence - Chapter 6, Combining Terms Using Boolean Operators, p. 46 onwards.
Advanced, detailed explanation in Online Searching : A Guide to Finding Quality Information Efficiently and Effectively - Chapter 7, Free Text for Recall in Subject Searches of Boolean Systems.
Checklist for things to consider when creating your search, based on the PRESS criteria covered later in this course: Cochrane EPOC checklist for developing a search.
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