Developing the search: combining terms
2004 version 2
24 May 2004
Combining terms
Two or more search sets can be combined to find their intersection (AND) or union (OR). Additionally a third Boolean operator NOT can be used to exclude items from an existing set. The operators may be used in upper or lower case.
Combining terms: and
It is possible to combine the coronary disease and wine concepts discussed in the MeSH searching section by using the combine icon - read more here. However it is quicker to type 1 and 2 in the enter Keyword or phrase box on the Main Search page:
Figure 31: Result of short-cut combination search using 'and'
Combining terms: or
An example of using the or combining operator is to find those articles containing cot deaths or sids in the title:
Figure 32: Short-cut combination search using 'or' in one step
This is displayed by the system as:
Figure 33: Result of short-cut combination search using 'or' in one step
Alternatively the two terms could be searched for separately and combined in a third search step as 1 or 2.
Combining terms: not
Combining searches using not will remove items in the second listed search set from those in the first listed search set. For example, type 2 not 1 to retrieve items with Glaxo in the title but not Wellcome:
Figure 34: Result of short-cut combination search using 'not'
Nesting
Ovid executes a command from left to right, so include in brackets (often called nesting) parts of your search strategy that you wish carried out together and before other parts of your search strategy. If you have more than one level of brackets the most deeply nested command is carried out first. In Figure 35 the coronary disease then prevention concepts are first combined using or and the results combined with wine using and by typing 1 and (2 or 4 or 5) and (3 or 6) in the enter Keyword or phrase box.
Figure 35: Final search history, after combining terms
If you wish to combine a series of search sets with and or or you may use the command syntax - for example and/1-2,7 or or/2,4,5 respectively.
Any questions? Please contact the MEDLINE Plus help desk:
Tel: 020 7383 6224 or 6737
email: info.medline@bma.org.uk
web: http://www.bma.org.uk/medline