Narrowing or Broadening a Search
For a review of sets as explained in Step 2, click here.
What is a good size for a set of records? Between 25 and 50 is recommended for most topics, but many students have settled for less, depending on how many references are required for a paper. If less than 25 records constitutes a set, you may wish to broaden the search by allowing additional terms with truncation or use of the OR operator (see below). More than 50 records may be cumbersome; after perusing a few, it may be evident that some are missing the mark. Use of limiters or the AND operator (also see below) might tighten the search.
Once you have received a set of records from a database, it may be connected to other sets by inserting the Boolean operators AND, OR, or NOT (aka AND NOT). Many CD ROM databases will supply a set number to accompany each set.
AND narrows a search by requiring each record to contain
all of the words submitted.
OR broadens a search by accepting records having any of
those words.
NOT narrows a search by deleting all records containing
the NOT word.
NOT is normally used only when a large number of false drops would be expected in its absence.
By querying the business database ABI/Inform with "marketing" we might expect to receive a set of, say, 1500 records represented by Circle A below. "Tobacco" might bring only 250 hits (records) represented by Circle B. Their intersection (C) represents perhaps 20 of all the records containing references to both "marketing" and "tobacco." The various combinations of the two terms linked with Boolean operators are shown below as they might appear in sets.
Once sets have been established, they may be referred to by number and manipulated in various combinations until a set of manageable numbers on the topic is produced, (e.g. #2 OR #4 AND #3 OR #6 AND #8).
NOTE: FirstSearch does not provide set numbers, and sets created earlier in the search cannot be recalled. Because fees to your library are based on each set found, it is best to submit connected terms in one search, e.g. marketing AND tobacco AND children.
Truncation is the act of removing word endings to broaden a search. The truncated word is followed by a truncation symbol, usually #,*, or ? depending upon which vendor interface is used.
By truncating "marketing" to "market#," the computer
would also pick up "market" and "marketer" plus their plurals.
Be judicious in applying truncation. Broadening a search too much may result in many false drops. In the above example, the search would bring up "flea markets" in addition to more pertinent items.
Limiting narrows a search by parameters such as the publication type (e.g. book, thesis, research article), geographic location for the topic, and date.
NOTE: limiting by date refers to the date of publication, not the date of an event being discussed. Online catalogs may provide limiting by collection (e.g. circulating, reference, reserve), by language, and by format (e.g. paper, microform, sound recording).
This can be accomplished with menus, with commands , e.g. FO [rmat] MI[croform], or with special indexes included with the database.
Use of a thesaurus to find descriptors was explained in Step 4 (click here for review).
It may additionally be used to broaden or narrow a search. This is accomplished by finding the relationship of a descriptor you used to other descriptors.
If you found few records in Psychinfo or PsycLit under the descriptor "Semantics," the Thesaurus of Psychological Index Terms indicates that you might broaden the search with "Grammar" (a Broader Term) or "Metaphor" (one of several Related Terms).
Likewise a search may be narrowed by selecting a Narrower Term from the thesaurus. It may also be narrowed by selecting the descriptor/s directly from the computerized thesaurus, which then searches only the subject fields.
Updated 3/20/99 by W. J. Frost