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A subject heading search, also known as a controlled vocabulary search, will search for articles on a given subject or topic rather than by looking for keywords within the text, i.e., an article will be tagged and indexed in a database as being about certain subjects. It is these subjects that are searched with this type of query.

Not all databases use the same subject heading catalog.

Pros

• Subject heading searches are easy to run.
• All articles produced should all be about the subject you have selected.
• In theory, you should receive more pertinent, albeit fewer, results than a keyword search. 

Cons

• Subject heading searches  will not always produce the most recent literature a database has to offer*.
• Only the bigger databases offer the utility of a subject heading search. All other databases will need to be keyword searched.

*Note: Due to the high volume of medical literature coming out every week, most databases, if not all, are several months behind at indexing articles. Until articles have been properly indexed by the database, they will not show up on a subject heading search. However, a keyword search will pick up articles as soon as they are uploaded to the database regardless of if they have been indexed yet or not

Putting phrases in quotation marks can make a huge difference to your search! Anything over one word is technically a phrase and should be placed inside "quotation marks." The reason for this is that databases are very literal; without the quotation marks, they will search for the terms quotation and marks separately. They do not understand that multiple words are part of the same phrase unless you tell them. 

For example, if you typed peanut butter and jelly day without quotation marks, the database would bring back every article with the word "peanut" in it, every article with the word "butter" in it, and so on...

In the example below, you can see that the phrase "peanut butter and jelly day" was not placed in quotations and Google Scholar brought back 27,100 results of which most were not pertinent. 

In the second picture the phrase was placed in quotations and only 23 results came back, but all were pertinent.

Note: When you put a phrase into quotation marks, the database will search for what's inside the quotations and ONLY what is inside the quotations. For example, a search for "aspirin vs. Tylenol" will fail to bring back articles where the author phrased this differently, e.g., "Tylenol vs. aspirin," or "aspirin versus Tylenol."

Phrases are highly specific. Be sure to consider all the different variations and make sure you include them in your search too.

Note: Some databases will not accept quotation marks and will assume that everything placed between two Boolean OR statements is a phrase, e.g., OR Tylenol vs Ibuprofen OR Ibuprofen vs Tylenol.

There are three Boolean operators: AND, OR, and NOT.

AND

The AND Boolean operator will reduce the amount of results a search yields as it forces the database to be more specific. For example, here the database will only return results that feature both the terms "peanut butter" AND jelly.

Tip: If you have too many results to wade through, try using an additional search concept with AND to get a smaller, more specific, batch of results.

OR

OR is used to add synonyms or alternate words to your search. By adding more synonyms to each concept you should get more results. A good rule of thumb is that OR is always more.

Here you can see that the database will bring back all articles that have either the phrase "peanut butter." or the word jelly, or both.

NOT 

The NOT  Boolean operator will purposefully exclude articles containing the specified search term(s.) 

NOT can be used to narrow down the desired meaning of a term that has different connotative meanings. 

Here you can see that the database will bring back articles about "peanut butter" — but if that article mentions jelly anywhere in the text, even randomly, the database will exclude that article from the results.

Tip: Use the NOT Boolean operator with care. You might lose the perfect article because it randomly mentioned the term you excluded. If you need to reduce the amount of results your search yields first try thinking of another search term and adding it to your search with an AND.

A Note on Capitalization

In our examples, you'll see that the Boolean operators are in all caps. Some databases require them to be in all caps, others do not. It's better to get into the habit of always capitalizing them so that it's easier to copy and paste your search terms from one database to another.

If you are building a search string with multiple concepts, added parentheses to your string helps to tell the database how to link the terms. So if you're building a search based on your PICO research question, and you have terms related to your population and your intervention, the parentheses group the terms to tell the database what to look for.

Example

Population terms

• Alzheimer's disease
• dementia
• cognitive impairment

Intervention terms

• hydration

Search string

("Alzheimer's disease" OR dementia OR "cognitive impairment") AND hydration

Larger databases allow users to limit their search by certain criteria, hence the name limiters.  Limiters are incredibly helpful and are usually found under the main search box or on the left hand side of the screen.

Pros

• Allows users to narrow down search results by various criteria. Useful limiters include:
  • Date range: Usually expressed by publication year or range, like the last ten years.
  • English language: Exclude articles in languages you may not understand.
  • Peer reviewed: Make sure the articles you are reading are from a peer-reviewed publication.
  • Study type: Specify if you want only systematic reviews, randomized controlled trials, etc.

Cons

• Limiters vary from database to database.
• Using too many limiters or poorly chosen limiters may bring back few results or poor quality results.

Note: Be aware of the full text limiter. It prevents you from seeing citations that might prove to be the perfect article for you. You can always request articles from other libraries via our free interlibrary loan service.

Fields are allocated spaces within a electronic article that are set up to store a specific type of information, e.g., the author field will be where author names are stored, and the title field is where the title of the article will be stored.

Field searching allows you to tell a database exactly where you want to look for your keywords. By default, the field search will be set to "All fields," meaning that your keyword search will check everywhere within an article's text for your specified keywords.

Here are some ways that field searching may be helpful:

• If you need more pertinent articles, limit your search to the title or abstract fields.
• If you're looking for a specific author, limit to the author field.
• If you're looking for a specific article, even if you only remember a few words of the title, limit to the title field.
• If you're searching on a specific topic, search the subject field. (Check out the subject searches tab above to learn the best ways to do this.)
• If you have an ISBN number, limit to that field.

Example of PubMed's fields:

Narrowing Results

To find fewer results:

• Add another concept using the AND Boolean operator. This will exponentially reduce the number of results you get back while making those results far more pertinent.
• Reduce the number of synonyms you are using. 
• Try a field search. For example, run a title field search.
• Use the NOT Boolean operator to select words that you do not wish to appear anywhere in the article.
• Use your limiters to:
  • Set a date range or reduce your date range.
  • Limit your results to a specific language.
  • Limit your results by article type, e.g., randomized controlled trials or systematic reviews

Broadening Results

To find more results:

• Add synonyms to your search string with the Boolean operator OR (remember, OR is more).
• Reduce the number of concepts in your search string by eliminating AND Boolean operators.
• Phrases are very specific; reduce or replace phrases with single keywords if possible.
• Use your limiters to:
  • Extend your date range.
  • Search more types of articles.