PubMed Tutorial : Creating a More Involved Search <!-- page title here --> Health Sciences Library System banner

Table of Contents
Overview of PubMed | Constructing a Simple Subject Search in PubMed |  Modifying a Search |  Creating a More Involved Search |  Using the Cubby to Save and Reuse Searches |  Using PubMed Features |  Getting From PubMed to Full Text Articles |  Using the Books Link

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PubMed Tutorial

Online Literature Sources for Evidence-Based Medicine

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Searching Specific Fields
Using Boolean Operators in the Search Box
Combining searches using History and Boolean Operators
MeSH and the MeSH Browser
Using Preview/Index

 

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Barbara Folb
Patricia Friedman


Creating a More Involved Search


Searching Specific Fields

Each PubMed/MEDLINE record contains many fields. You can choose to search for terms within a specific field to refine your search.

Principles:

  1. A list of all Search fields is in PubMed Help : Search Fields Descriptions and Tags. It can also be reached by clicking on the word Help in the blue bar to the left of the PubMed screen, then choosing Search Field Descriptions and Tags under the References section.
  2. A range of dates can be searched in any date field.
  3. Search fields are indicated by putting the field abbreviation in square brackets [ ] after the search term.
  4. Using fields turns off the PubMed Automatic Term Mapping.
  5. Common reasons for searching a specific field are:
    1. To reduce the number of records retrieved
    2. To focus the results of a search. For example, a word appearing in the title of an article is more likely to be a major topic than one appearing only in the abstract.

Examples:

Enter the following two searches and compare the results and the search details:

  1. congestive heart failure [ti]
  2. congestive heart failure
Modify the last search by searching for articles published between 1998 and 2001:

  1. congestive heart failure AND 1998:2001[dp]
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Using Boolean Operators in the Search Box

Using three the Boolean operators used in PubMed - AND, OR, NOT - and parenthesis, you can clarify the relationship between your search concepts and control your search results more precisely.

Principles:

  1. Operators must be in capital letters for PubMed to recognize them.
  2. AND is used to indicate that two terms must both appear in any records retrieved. This results in fewer records retrieved.
  3. OR is used to indicate that either one of two terms must appear in any records retrieved. This results in more records retrieved. It is most often used to include synonyms for the same concept in the statement.
  4. NOT is used to indicate that a term may not appear in any records retrieved. This results in fewer records retrieved, and should be used with caution, since you may unintentionally exclude records that are useful.
  5. Various combinations of operators can be used in a single search statement.
  6. Parenthesis are used like they are in algebra to indicate to PubMed in which order to process the search terms. If no parenthesis are used, PubMed processes the terms and operators from left to right.

Examples:

Using AND:

  1. AND is the default operator if no operators are entered in a search statement. Because of this, you do not need to type it out unless:
    1. It is needed to clarify grouping of words.
    2. You do not want any of the words to be interpreted as a phrase.
  2. Example: Enter the following searches and compare the Details of each.
    1. drug carriers hepatitis
    2. drug AND carriers AND hepatitis
Using OR:

  1. Use OR to expand a search by using several terms to express a single concept or related concepts.
  2. This is especially useful if you are searching in specific fields, and the Automatic Term Mapping is disabled.
  3. Enter the following two searchs and compare the number of records retrieved:
    1. peptic ulcer
    2. peptic ulcer OR stomach ulcer OR duodenal ulcer
Using NOT:

  1. Use NOT to exclude terms from a search.
  2. Use NOT with caution. You may remove relevant articles from your results.
  3. NOT is a good tool to use in conjunction with the History feature to combine previous searches in new ways. See Combining searches using History and Boolean Operators in this document for more information.
  4. Enter the following searches and compare the search results:
    1. hypertension AND practice guidelines
    2. hypertension AND practice guidelines NOT esophageal varices
Using Parentheses to Clarify Search Statements:

  1. Use parentheses to group search terms.
  2. PubMed searches terms inside parentheses as a unit. Without them the operators are executed from left to right in the search statement.
  3. Enter the following searched and compare the search results and details:
    1. pharmacotherapy AND peptic ulcer AND rational OR objective
    2. pharmacotherapy AND peptic ulcer AND (rational OR objective)
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Combining Searches using History and Boolean Operators

Using the History feature, you can recombine previous search statements with Boolean operators.

Principles:

  1. History stores all your search statements during the current session.
  2. History stores searches until one hour of inactivity passes, when it erases them.
  3. When recombining search statements, refer to them by number proceeded by a # sign.
  4. There is a new button to choose after the search entry box, Preview. Use Preview if you want to see how many records recombined searches will retrieve without actually running the search. Use the Go button if you want to actually run the search and skip the Preview.
  5. You can rerun any search in the History by clicking on the number of records retrieved after the search statement.
  6. One approach to searching involves entering all your search concepts as separate searches, then using History to combine and recombine them. This can be a very efficient way to structure a search session.

Examples:

  1. Enter and run the following 2 searches separately:
    1. hypertension
    2. practice guidelines OR meta analysis OR metaanalysis OR metanalysis OR clinical guidelines
  2. Click on the word History under the search entry box.
  3. Note that all your current search statements are listed here.
  4. Combine the two searches entered above with the operator AND by:
    1. finding the numbers in front of them
    2. Entering those numbers proceeded by # in the search entry box. It should look like this: #1 AND #2. Actual numbers used will vary depending on how many searches you have done.
    3. Click on Preview.
    4. Look at the new search in the History list.
    5. Click on the number of records retrieved after the latest search statement to run the search.
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MeSH and the MeSH Browser

MeSH is the controlled vocabulary assigned by the National Library of Medicine indexers to records representing articles . MeSH pulls together articles that use different terms to refer to the same concept by assigning one MeSH term to each article covering the concept. The MeSH browser makes it easier to identify the MeSH headings associated with a concept, and to build a search using multiple MeSH terms.

Principles:

  1. Searching using MeSH terms instead of text words retrieves fewer citations, but more of them will be pertinent to your topic.
  2. MeSH terms are organized in a hierarchy of broader and narrower terms.
  3. PubMed defaults to exploding a MeSH search. This means that all narrower terms under the MeSH term chosen will be included in the search results unless you specifically indicate that they should not be included.
  4. MeSH terms have associated subheadings, such as etiology, pathology, adverse effects, etc. By default all are heading/subheading combinations are retrieved in a search unless you choose specific subheading(s) to include. You may choose any number.
  5. The search entry box that appears in the MeSH Browser only searches the MeSH, and does not directly search PubMed.
  6. The MeSH Browser will attempt to map your search terms to the MeSH headings.
  7. If your term does not find an exact match in the MeSH, you are offered possible terms to try.
  8. A search including multiple MeSH terms can be built from within the MeSH Browser before running the search in PubMed.
  9. To return to PubMed from the MeSH browser without actually running a search from the MeSH browser, click on the word PubMed in the black bar across the top of the screen.
  10. PREMEDLINE records will not be retrieved in a MeSH search, since they haven't been assigned yet.
  11. MeSH is updated annually. There is a time lag before new concepts will appear in MeSH.

Examples:

  1. Access the MeSH browser by clicking on MeSH Browser under PubMed Services in the blue bar at the left of the screen.
  2. Enter heart failure in the search entry box.
  3. You will be given some terms to choose from. Choose Failure, Congestive Heart by clicking on it to highlight it , then clicking on Browse this term.
  4. A screen appears that shows the term you chose in the context of its broader and narrower terms.
  5. Click on the [Detailed display] link.
  6. A screen appears where you can modify the term with several choices:
    1. Choose the subheading drug therapy by clicking in the box in front of it.
    2. Choose Restrict Search to Major Topic headings only by clicking in the box in front of it.
  7. Click on the Add button.
  8. A new screen appears in which a PubMed search is being built, but hasn't been run yet.

  9. Do another search of the MeSH browser for: beta blockers.
  10. Again you will be given terms to choose from. Choose beta-Andrenergic blockers as done above.
  11. The MeSH heading is Adrenergic beta-Antagonists. Note the long list of more specific drugs listed as narrower terms under this heading.
  12. Click on the Add button with the operator set to AND. Note the new search statement that appears.
  13. Click on PubMed Search to run the search. You will exit the MeSH browser and return to PubMed.
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Using Preview/Index

The Preview/Index feature combines two separate but related features. Preview allows you to see how many records will be retrieved with a search statement before running the search. Index allows you to find words occurring in PubMed records either anywhere in the record, or in a particular field, and how many times they occur.

Examples:

  1. Click on the words Preview/Index below the search entry box.
  2. In the next screen, enter the words beta blocker in the second (new) search box near the bottom of the screen.
  3. Click on Preview. A new search will appear in the middle of the page under Most Recent Queries telling how many records that search will retrieve.
  4. Type beta blocker in the second search box again. This time click on Index.
  5. A new box appears listing terms from the phrase index that start with beta blocker.
  6. You can choose one or more to add to your search. Click on a term to highlight it. If more than one term is wanted, hold down the Ctrl key while clicking on the terms.
  7. Clicking on the AND, OR or NOT buttons above the terms listed will add the term(s) selected to the search entry box at the top of the screen. Highlight beta blocker and click on AND.
  8. The default is to search for a term in all fields. You can choose a specific field to search by clicking the down arrow next to All Fields. Do that now and choose Title Word.
  9. Enter beta blocker again, and click on Index. You will get a smaller number of hits than searching All Fields.
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This page was updated on April 19, 2001.
Pages maintained by Barbara Folb folb@pitt.edu