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What you need to know to get started with your research at the ISU Library.

Research 101: Searching is Strategic

About Searching Databases

Search engines in databases and on the Internet vary in how you use them depending on how they are built and designed. But there are common search features and functions that occur. Learning about the different features can help you craft a successful search strategy to retrieve what you need.

Rules of Thumb

These are common rules of databases. Your database may not follow them.

Use parentheses to group complicated search requests.
Use quotation marks to group phrases.
The most common truncation symbols are * and ?
Most databases use AND as a default Boolean term.
Capitalize Boolean terms.

Boolean Operators


Most databases allow the user different searching methods. One of the most common searching methods is Boolean Searching, also called keyword searching. This type of search tells the database to retrieve all of the records in the database which contain a word or a set of words. You can alter the results by using Boolean Operators which are the words AND, OR and NOT. See below for an explanation of these terms. Some databases require the Boolean operators to be capitalized or they are searched just like regular search terms.


Example: cookies AND milk

Will retrieve records which contain the word “cookies” and the word “milk.” This operator is used to lessen the number of records retrieved. This is the most common default Boolean term.


Example: caffeine OR coffee

Will retrieve records which contain the word “caffeine” or the word “coffee.” This operator is used to broaden the number of records retrieved.


Example: chocolate NOT cake

Will retrieve records which contain only the word "chocolate" but not the word "cake." This operator is used to reduce the number of records retrieved.


Use to preserve the “logic” of your Boolean Search. Nesting is the use of parenthesis to put your search words into sets. The database first does the search within the parentheses. If you do not use parentheses, Boolean terms are connected according to the default functions of the database search engine. Because it is difficult to keep track of differences in databases and because almost every database accepts parentheses, it is suggested that parentheses ALWAYS be used in a complicated search phrase.

      (Huntingtons AND disease) OR chorea     

      Huntingtons AND (disease OR chorea)

      ((diabetes OR diabete) AND (hypertension OR (high blood pressure))) NOT therapy


Use to find different forms of words in a Boolean or keyword search. Some databases use the asterisk, some use a dollar sign, and others use the question mark. The symbol may represent one character or they could represent multiple characters. They usually apply to word endings. They may or may not apply at the beginning or middle of a word. Check the help function of the database you are using to learn the truncation symbol and rules.

        Neuron*                    Will retrieve neuron, neurons, neuronal, 
, etc.

The most common truncation symbols are * and ?


Stopwords are commonly used words that occur too frequently in records so as to be unhelpful. They will either be ignored and not searched by a search engine, or they will automatically stop or prevent a computer keyword search. Stop words are usually listed in the Help screens of whatever rch engine you are using. Commonly used words rarely help refine your search results.

Examples of common stop words are: the, an, at, for, from, of, then.

Phrase searching can sometimes force a search engine to search for a stopword, depending on the search engine.


Phrase Searching

Phrases are treated differently in databases. Some automatically assume two adjacent words are a phrase. Others require the use of quotation marks or parentheses to search for a phrase. Databases that automatically assume two words are a phrase often ignore the quotation marks if they are unnecessary. Because it is difficult to keep track of differences in databases, it is suggested you use quotation marks when you enter a phrase.

"common cold"

"shortness of breath"      (View Stopwords to avoid a possible
                                                 pitfall from "of.")

An exact phrase finds the words in exactly the same order.

“Heart attack” 

“attack heart”


Many databases contain a thesaurus. This is a directory of assigned Subject
{eg. Medical Subject Headings (MeSH)}. Searching for a subject
heading instead of a word that
happens to appear anywhere in a record can
reduce the number of irrelevant records retrieved from your search. Some
databases will automatically include synonyms in the search, whether you
want them to appear or not, so check the rules. This is called thesaurus mapping.

        Cancer                               Finds cancer and neoplasm when thesaurus
                                          mapping occurs.

        "heart attack"               Myocardial Infarction is searched as a MeSH term
                                          in addition
to “heart attack” being searched as text

Subject Headings

Most databases assign subject categories in a hierarchy from general to specific. 
Medical Subject Headings (MeSH) are hierarchical. To Explode a Subject Heading 
in a search includes all subject headings subordinate to the Subject Search Term. 

  • Dogs
    • Terrier
      • Fox terrier
      • Bull terrier
    • Hound
      • Bassett hound
      • Blood hound

A search for the following term in MEDLINE or CINAHL retrieves the following results.  

Terrier                         matches records with Terrier as a subject heading

Terrier (Exploded)      matches records with Terrier, Fox terrier, and Bull terrier
                                 as subject headings   

Subject headings are VERY important in searching health science databases.
CINAHL and MEDLINE are specifically designed to be searched using the
subject headings.   


The Index is the list of words used by all the records in a database. A database does not directly search its records but actually searches its Index for your word(s), which then tells the database which records contain those words. Some databases allow you to browse the Index directly. The PubMed database contains four separate indexes: a Phrase Index, a Journal Title Index, an Author Names Index, and MeSH Headings.

Stopwords are not included in the database. That is why they cannot be searched.

Failed Searches

Studies of medical information searches have identified common mistakes made. 

Questions to Ask Yourself After a Failed Search
Did you misspell any words?
Are there too many ANDs? (They reduce results.)
Unnecessary addition of author’s name?
Punctuation? Used or not used?
Truncation error? Wrong symbol? Wrong placement?
Incorrect phrasing of title?
Did you misremember the title?
Inappropriate use of specialty headings?
Incorrect use of subheadings?
Not using related terms to catch missed concepts (text words or MeSH terms)?
Low-frequency terms?
Using general terms instead of subheadings?
Accidentally searching title instead of keyword?
Incorrectly understanding system defaults (default OR, for example)?
Incorrectly understanding search hierarchy in PubMed?
Concepts searched not in document?
Using synonyms or acronyms?

Most Common OVID MEDLINE Searching Mistakes

Professor Katherine Schilling of IUPUI has researched medical students search strategies and found that these were the 10 most common research mistakes in Ovid MEDLINE.

Listed in order by when they occur in the search process:

1. Failure to properly translate research/clinical question into a searchable strategy
2. Selecting the wrong database (i.e., selecting a 
Full Text database rather than the larger MEDLINE database)
3. Approaching a MEDLINE search like it's Google or Yahoo
4. Failing to identify the appropriate MeSH  term(s)
5. Failing to explode a MeSH term
6. Misunderstanding the relationship between "explode" and "focus"
7. Misapplication of subheadings to a MeSH term (i.e., applying 1+ specific subheadings when applying ANY would be a more effective strategy)
8. Misuse of the Boolean AND and OR
9. Misapplication of limiters (i.e., usually applying too many of the wrong limiters; entering check tags (limiters) as subject headings; applying inappropriately to "full text"
10. Failure to interpret search results and modify strategy appropriately

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Key Links

Search Strategies

Search Strategies

Focus or narrow the Search; Finding Fewer Quality Publications

  • Use the Subjects of the database to find publications about a specific subject. (Could increase the results.)
  • Limit to the highest levels of evidence of Evidence-Based Practice.
  • Limit to the newest results.
  • Search for your words in the title of the publication.

Broaden the Search; Finding More Publications

  • Combine synonyms with OR
  • Search for spelling variations. Example behavior OR behaviour
  • Search for a broader topic that includes your topic. Example, books on baseball would include entries about Jackie Robinson.
  • Use references to find other sources. (backward in time.)
  • Use the Web of Science database to find journal articles that cite a specific article. (forward in time)

More Strategies

  • Search for publications on parts of your topic. If your topic contains components A+B+C+D, then look for article that include A+B+C. Or A+C+D. Or A+B or A+C... Do you understand?