Step 3: Build your search strategy
>> Searching with subject headings and keywords
>> Searching with operators, parentheses, truncation symbols, and advanced searching tips
After selecting the database(s) you will use, it is essential to develop your search strategy. Your search strategy will guide you in finding relevant information in your chosen databases. The key to this process is identifying and utilizing a combination of keywords, subject headings, search operators, and limiters.
It can be helpful to keep track of your key concepts and terms as you go. To do this, you might consider using a search strategy worksheet to organize your process.
Subject headings are assigned descriptors, similar to hashtags, but from a controlled vocabulary, which can sometimes be found in a database's thesaurus. They are used in some databases to capture a concept uniformly. Searching with these standardized words or phrases, instead of text words, efficiently captures all the information falling under that term. This means you don't need to worry as much about synonyms and spelling variations.
Remember to keep in mind:
⇒This is important to note because if you search using only subject headings, you might miss records or articles that haven’t been indexed with them yet.
For thorough searches, you would generally include subject headings, their text word equivalents, and any alternative terms (related terms, broader terms if needed, specific terms, synonyms, alternative spellings or variants, abbreviations).
For example:
***However, your term may not always yield appropriate subject headings. In such cases, it is best to search your term as a keyword.
Keyword searching (also called textword, natural language, or free-text) is when you search for words you expect to find in the title, abstract, or author-assigned keywords. Remember, most article databases do NOT search the full text. Create a list of keywords or phrases based on the main concepts in your research question. You can organize this using the search strategy worksheet above, or any layout that works for you. When using this technique, be aware of synonyms and spelling variations.
While subject headings are usually the foundation of search strategies because they can capture a vast amount of information, there are various reasons why you should add keywords to a search:
For an emerging research topic that may not yet have a subject heading to describe it.
To retrieve the most recent articles (which have not yet been indexed with subject headings).
Occasionally, articles can be incorrectly indexed (e.g., not assigned a relevant subject heading) and may be missed by a search using only subject headings.
To develop a thorough search strategy for a systematic review or other knowledge synthesis, we always supplement the search with keywords.
***You should keep in mind that keywords do not generally account for:
⇒ Truncation symbols and operators can help with this.
⇒ However some databases do include lemmatization.
|
Subject Headings |
Keywords (also called textwords, natural language terms, or free-text terms) |
|---|---|
|
Pre-defined "controlled vocabulary" terms |
Natural language terms used by authors in the title, abstract, or author keyword fields (may also be terms used in full text) |
|
Need to know the exact controlled vocabulary term |
Need to use the textword equivalents of the subject headings plus alternative terms |
|
Less flexible. Not always an appropriate subject heading available: May need to combine more than one subject heading with AND to capture one concept or combine subject headings with OR when multiple subject headings could be considered synonyms of the same concept |
Quick & flexible way to start exploratory searches |
|
Database looks for subjects only in the subject heading or descriptor field |
Database looks for terms in selected fields, e.g., title/abstract/author keywords (many databases also allow searching in other fields such as in the affiliation field or publication source field) |
|
Highly relevant results |
Generates irrelevant results but can increase the sensitivity of the search (i.e., can pick up records that the subject headings may have missed) |
Using a concept map we will demonstrate how to use subject headings and keywords with the following research question:
⇒ What specific occupational risks are associated with an increased cancer risk in firefighters?
***Subject headings were chosen according to MeSH terms in MEDLINE
| CONCEPT 1 | CONCEPT 2 | CONCEPT 3 |
|---|---|---|
|
Occupational risks
►Subject Headings Occupational exposure Environmental exposure Keywords Occupational Risk / Occupational risks / workplace hazard / workplace hazards / chemical exposure / contaminant / contaminants
|
Cancer
Subject Headings Neoplasms Keywords cancer / cancers / cancerous / malignancies / malignancy / malignant / metastasis / metastases / metastatic / neoplasia / neoplasm / neoplasms / neoplastic / tumor / tumors / tumour / tumours etc. |
Firefighters
Subject Headings Firefighters Keywords firefighter / firefighters |
► in Ovid MEDLINE, occupational risks mapped to several subject headings, and based on the scope note these are the most relevant. See the scope note for Occupational Exposure below:
Boolean operators can be placed between your search terms to narrow or broaden a search, or to exclude certain terms. The most common Boolean operators are OR, AND, and NOT.
Remember to keep in mind that:
Note: Capitalize your operators as a matter of practice. In some platforms or search systems, it does not matter whether you enter them in uppercase or lowercase, but others (like Google Scholar) require them to be in uppercase to work properly.
| OR |
|
|---|---|
| AND |
|
| NOT |
|
Many bibliographic databases also support the use of proximity operators, also known as adjacency operators. These operators allow you to refine your search by specifying the proximity of your search terms, identifying the number of words near or between them.
For example:
Parentheses (or brackets) are used to set the order of the execution of Boolean logic in a search. When combining different search terms with Boolean operators, the database doesn't automatically recognize synonyms. By using parentheses to group similar terms, you can ensure they are treated as a single unit in your search.
For example:
(chest OR thorax OR thoracic) AND (imaging OR radiographs OR radiography)
To demonstrate the impact of searching using parentheses see the image below:
Truncation symbols are shortcut characters which can help to include variations of your text word without having to type each variation into the search separately. This feature is also known as stemming.
The asterisk, *, is the most common truncation symbol. Other truncation symbols and wildcards include, #, ?, $, !. Depending on the platform you are using to search a given database (e.g., EBSCOhost, Ovid, ProQuest), other truncation and wildcard symbols may be available to use. Please see the database-specific operators and fields for more information.
For example:
Searching for computer*, searches for computer, computers, computerised, computerized, etc.
Advanced search techniques can include quotation marks (" ") to force phrase searching or to turn off lemmatization (this is database-dependent) and specifying search fields (such as title, subject, etc.).
Example of using quotation marks:
Imagine you're researching the phrase adverse drug reaction:
Without quotation marks: Searching adverse drug reaction will find articles that include the words adverse, drug, or reaction—but these words can appear anywhere in the text and in any order.
With quotation marks: Searching "adverse drug reaction" will find articles where these three words appear together in exactly this order.
Example of using search fields:
When you're researching the phrase adverse drug reaction, you can use a search field to focus your results
Searching without a field: Searching "adverse drug reaction" will give you results from anywhere in the article—titles, abstracts, body text, etc.
Searching with a field: Searching TI: "adverse drug reaction" tells the database to find articles where the phrase adverse drug reaction appears specifically in the title.
***Each database is different, so be sure to consult our database-specific tables to check for exact field codes and additional functions.
When searching in databases, there are several ways to structure and organize your searches to make them more efficient and concise. The following simplified examples of searching in PubMed illustrate different options you could use if you were looking for literature on the use of ultrasound to diagnose pulmonary tuberculosis.
Please note: Depending on the database you're using, you may see different ways to combine search line numbers (for example, #1 OR #2 in PubMed, or S1 OR S2 in CINAHL).
"Line by line" -- Easier to see if you have made spelling mistakes when you look at the number of records generated by each line; not all databases allow you to enter searches this way as it requires access to a search history (Example screenshot from PubMed):
"Block by block" -- One key concept or set of terms per line: More succinct but you must check even more carefully for spelling mistakes; once again, not possible in all databases (requires access to a search history) (Example screenshot from PubMed):
"Single line" -- Many databases will allow for this type of entry, but you must check that parentheses (and intended application of Boolean operators, in some cases) are supported (Example screenshot from PubMed):
Please note: While this guide is managed by the Schulich Librarians, the contents of the guide were developed in collaboration with Yvon-Tani Jackson, MISt student (2026).
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