PubMed Search Rules and Syntax

Excerpted from the NLM Technical Bulletin, November-December 1997

Boolean Syntax:

  1. Boolean operators, AND, OR, NOT must be entered in UPPERCASE. Please note that the ELHILL connector "and not" is simply the single word NOT on PubMed.
    Because PubMed only recognizes Boolean operators in uppercase, it is no longer necessary to use a symbol to disguise MeSH terms that contain Boolean operators. For example, the MeSH term Wit and Humor must be entered in ELHILL as wit a#d humor using the hash mark to "hide" the word and. But in PubMed you simply enter wit and humor [mh].

  2. PubMed processes all Boolean connectors in a left-to-right sequence. You can change the order in which PubMed processes a search statement by enclosing an individual concept in parentheses. The terms inside the set of parentheses will be processed as a unit and then incorporated into the overall strategy. On ELHILL, all AND statements are processed first.

  3. When you enter a Boolean search statement, PubMed will automatically parse the search terms on either side of the Boolean operator into a single phrase. For example, cigarette smoking AND therapy will only search for cigarette smoking as a phrase, not cigarette AND smoking AND therapy.

    In addition, if PubMed finds a phrase within a search strategy string that uses unqualified terms it will automatically search the terms as a phrase rather than simply combining them. For example, if you enter air bladder fistula in the PubMed query box, PubMed will search "air bladder" as a phrase. If you do not want this automatic phrase parsing enter each term separated by the Boolean operator AND, e.g., air AND bladder AND fistula.

    Truncation:

    1. To truncate a term, use an asterisk (*) at the end of a search term. For example, bacter* will retrieve bacteria, bacterium, bacteriophage, etc. OR'd together automatically. Whereas on ELHILL, in addition to using the colon truncation symbol, you have to use the instruction word "all" to avoid getting an ELHILL Multi-Meaning message (e.g., all bacter:).

      Note: There is no single-character truncation symbol such as the pound sign (#) used on ELHILL.

      Date and Date Range Format:

      1. Dates or date ranges must be entered using the format YYYY/MM/DD [dp], e.g. 1997/10/06 [dp] . The month and day are optional (e.g., 1997 [dp] or 1997/03 [dp]). To enter a date range, insert a colon (:) between each date (e.g., 1993:1995 [dp] or 1997/01:1997/06 [dp]).

        Note: To specify a publication date or range, it is recommended that you search only by year (e.g., 1996 [dp] or 1995:1997 [dp]). Journals vary in the way the publication date appears. Some journals include just the year, whereas others include the year plus month or year plus month plus day. And, some journals use the year and season (e.g.,Winter 1997). The publication date is recorded as it appears in the journal.

        Search Field Qualification:

        Terms can be qualified using PubMed's search field tags. Note: A list of search field tags is available in PubMed's online help under Search Fields.

        1. Terms must be post-qualified, such as aromatherapy [mh] not [mh] aromatherapy.
        2. Search field tags must be enclosed in brackets, e.g., [mh] not (mh).
        3. Case does not matter nor does spacing, e.g., crabs [mh] = Crabs[mh].
        4. Terms that are qualified with the Text Words field tag [tw] will be searched for in the Title, Abstract, MeSH headings and Subheadings, and Names of Substance. Whereas, on ELHILL Subheadings are not included in a Text Word search. Some additional fields will be added to PubMed's [tw] soon.

          MeSH Terms, Subheadings, and Language

          MeSH Terms:

          1. MeSH Terms must be qualified using the search field tags, e.g., [mh] for MeSH Terms or [majr] for Major MeSH Topic. The asterisk (*) which on ELHILL is used for MeSH Major Topic is reserved for truncation in PubMed.

          2. MeSH terms are automatically exploded to include the more specific terms. The ability to turn off this automatic explosion is coming soon to PubMed.

            Note: Searching with MeSH terms will exclude PREMEDLINE citations as they have not yet been indexed with MeSH.

            Subheadings:

            1. You can directly attach subheadings using the format MeSH Term/subheading (spelled out), e.g., neoplasms/diet therapy [majr]. The ability to use the two-letter subheading abbreviations will be available soon. In addition, only one subheading may be directly attached to a MeSH term, e.g., neoplasms/diet therapy [majr] OR neoplasms/drug therapy [majr]

            2. The Subheading field and search field tag (e.g., [sh]) will be available soon in PubMed so that multiple Subheadings can be "free-floated" in a search strategy.

              Language:

              1. Language must be spelled out. The 3-character abbreviation search (e.g., eng) is coming soon to PubMed.

                Note: The ELHILL expression "and not for (la)" was devised to aid in computer efficiency. Negating about 25% of MEDLINE citations (those that are foreign language) is much more efficient and less costly than limiting to 75% of MEDLINE (those that are English) on ELHILL. This shortcut is not necessary on PubMed. So, you can now use the syntax AND english [la] on PubMed without worrying about overloading the system.

                Latitudes, March/April, 1998 -- Vol. 7, Number 2