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Systematic Reviews for Health: 7. Boolean Operators

A guide on how a Research Librarian can help you during a systematic review process

Step 7. Boolean Operators

Once all free-text terms and controlled vocabulary terms have been identified, you can start the proper searching process. It is recommended to search for each identified search term individually, then use the correct Boolean operators to combine the terms. This will help prevent any human errors. It also allows you to see which search terms add value to the search and if a particular search term produces too many irrelevant results.

Boolean Operators Explained

OR

An OR search will find information which includes either search term. All free text and controlled vocabulary terms identified for a concept are to be combined with an OR. This is to broaden the search and to capture all articles on a topic regardless of which term is used in the article.


AND

An AND search will find results with information common to both search terms. Once all relevant information for each concept has been found, the concepts are joined with AND. This is to narrow the search and to only capture articles in which all concepts appear.


NOT

A NOT search will exclude words from your search results. This is to narrow your search, telling the database to ignore concepts that may be implied by your search terms. If you are interested in e.g. only finding human studies you may be tempted to type NOT animals. This means that articles that include the word animals are excluded, including studies on animals as well as humans, which potentially are relevant. As a NOT search has the potential to exclude relevant articles, it is not normally recommended for a systematic review. 


NOTE!  All databases support these Boolean operators. The syntax for the NOT operator may vary slightly. For more information visit the Search Help menu within the relevant database or see

Example - In General

Combine all terms within a concept with OR. Then, join the searches for each concept with AND.

Example - In Detail

This is how you could approach the example in Medline via Ovid:

1. Carry out separate searches for each free-text term and controlled vocabulary term in Concept 1 of Concept Table.

To search for MeSH terms, use Search Tools section to Map Term. To search for free-text terms, use Search Fields section and tick relevant fields, e.g. Title, Abstract, Keyword Heading Word.

1  Dementia.ab,kf,ti.
Alzheimer.ab,kf,ti.
3  "Huntington*".ab,kf,ti.
Kluver.ab,kf,ti.
5  Lewy.ab,kf,ti.
6  exp Dementia/

NOTE!  In Ovid you need to tick a box if you want to explode a MeSH term; the default is non-explode. This is different to PubMed.

2. Combine all individual searches for Concept 1 with OR:

1 or 2 or 3 or 4 or 5 or 6

Either type as above, or select searches 1 to 6 and click Combine with OR.

3. Repeat steps 1 and 2 for all other concepts.

4. Combine the OR searches for each concept with AND.

44  7 and 22 and 31 and 43

Either type as above, or select searches 7, 22, 31 and 43 and click Combine with AND.

This is how you could approach the example in Medline via PubMed:

1. Carry out separate searches for each free-text term and controlled vocabulary term in Concept 1 of Concept Table.

In PubMed Advanced Search, change the drop-down menu to Title/Abstract or MeSH Terms accordingly, then enter each search term and Add to History (change Search drop-down)

#1  dementia [tiab]
#2  alzheimer [tiab]
#3  huntington* [tiab]
#4  kluver [tiab]
#5  lewy [tiab]
#6  dementia [mh]

NOTE!  There is no option for non-exploded MeSH term in the drop-down menu. If you want to not explode a MeSH term, keep the drop-down default of All Fields and use this syntax in the search box: Dementia[MeSH:NoExp] or dementia[mh:noexp]

2. Combine all individual searches for Concept 1 with OR:

#7  #1 OR #2 OR #3 OR #4 OR #5 OR #6

Either type as above, or use the Add Query / Add with OR  link in the History under Actions to bring the individual searches back up into the Query Box. This will give you search #7

(((((Dementia [tiab]) OR Alzheimer [tiab]) OR Huntington* [tiab]) OR Kluver [tiab]) OR Lewy [tiab]) OR Dementia [mh]

3. Repeat steps 1 and 2 for all other concepts.

4. Combine the OR searches for each concept with AND.

#49  #7 AND #24 AND #34 AND #48

Either type as above, or use the Add Query / Add with OR link in the History to bring the individual searches back up into the Query Box. This will give you search #49:

(((((((((Dementia [tiab]) OR Alzheimer [tiab]) OR Huntington* [tiab]) OR Kluver [tiab]) OR Lewy [tiab]) OR Dementia [mh])) AND ((((((((((((((((Animal-assisted therapy [tiab]) OR Animal-assisted activit* [tiab]) OR Animal-assisted intervention* [tiab]) OR Animal therapy [tiab]) OR Pet therapy [tiab]) OR Dog therapy [tiab]) OR Dog-assisted therapy [tiab]) OR Canine-assisted therapy [tiab]) OR Aquarium [tiab]) OR Animal Assisted Therapy [mh:noExp]) OR Pets [mh]) OR Dogs [mh]) OR Cats [mh]) OR Birds [mh:noexp]) OR Bonding, Human-Pet [mh]) OR Animals, Domestic [mh:noExp])) AND (((((((((Music therapy [tiab]) OR Music* [tiab]) OR Singing [tiab]) OR Sing [tiab]) OR Auditory stimulat* [tiab]) OR Music [mh]) OR Music Therapy [mh]) OR Acoustic Stimulation [mh]) OR Singing [mh])) AND ((((((((((((Aggression [tiab]) OR Neuropsychiatric [tiab]) OR Apathy inventory [tiab]) OR Cornell scale [tiab]) OR Cohen Mansfield [tiab]) OR BEHAVE-AD [tiab]) OR CERAD-BRSD [tiab]) OR Behavior* [tiab]) OR Behaviour* [tiab]) OR Aggression [mh]) OR Personality inventory [mh]) OR Psychomotor agitation [mh])

Need More Help?
Book a consultation with a Learning and Research Librarian or contact Librarians@utas.edu.au.