is determined. Specific terms that apply to the determined subjects are chosen
from the standardized list, regardless of the terminology used by authors. This
approach provides a consistent method for retrieving the records even when
different terminology is used in the text. For example, the term heart attack
is always listed as “myocardial infarction” within a controlled vocabulary
structure. Using controlled vocabulary searching is called subject searching.
Unless otherwise noted, only records that match exactly to the terms as they
were entered are displayed. The challenge is to determine which term is being
used to represent the subject matter that is being sought.
It is possible to find standardized lists used in databases to determine the
best terms to use. In most databases, terms are hyperlinked for ease of use. Do
not assume that a keyword in one database is the same one to use in another
database. For example, a search conducted in the PsycINFO database may use
a different subject term than a search conducted in the MEDLINE database
would use, even though both are science-related databases. When this happens,
the search “fails” and the searcher is mistakenly led to believe that the second
database contains no information on the topic.
Exploding is one of the most powerful techniques for searching subject
headings. When a subject term is exploded, the database is instructed to search
all the records indexed to that term as well as any terms that are in a related,
narrower category. For example, exploding the search term “headache” in a
CINAHL search results in a search that includes the terms “rebound headache”
and “vascular headache.” Exploding can dramatically increase the number of
records generated by the search. Most health sciences databases support this
technique.
One of the benefits of knowing both keyword and subject searching is that
they can be combined to increase the effectiveness and efficiency of the search.
Qualification and positional operators are more advanced keyword techniques
that can be very powerful when used in combination with subject searching.
Qualification designates which fields are to be searched in the record. The
most common ways to limit searches are by author (au), title (ti), subject (su),
publisher, and publication date. Placement of the punctuation can be important
when using limiting search terms. These options may be available only using
the advanced search methods in databases.
The proximity of search terms to one another can be specified using
positional operators. The most commonly used are “adj” (adjacent), “near,”
and “same.” Usually, “adj” and “near” can be grouped with a number to specify
the number of words that can appear between search terms. “Same” designates
that the search terms are found in the same field of the record such as the title
or the abstract. Because order is not designated with “same,” search terms will
KEY TERMS
subject searching:
Searching
databases using
controlled
vocabulary
exploding:
Technique for
searching subject
headings that
identifies all records
indexed to that
term
qualification:
Limiting fields of
search, commonly
using limits such
as author, title, or
subject
positional
operators: Terms
that specify the
number of words
that can appear
between search
terms4.4 How to Search for Evidence 115