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Systematic Reviews for Health: 8. Search Limits

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

Step 8. Search Limits in Databases

Once the final search has been done, combining all concepts with AND, you may refine the search results further, e.g. by publication date, study design.

It is generally not advisable to use the limit options that the databases provide:

  • Using these limits you will only be able to find articles that have been indexed. However, not all articles in the databases are indexed (yet).
  • The Human filter is especially discouraged.
  • You need to be able to justify any limit you add to your search, including the language and date limit.

TIP!  It is a better option to make the desired refinement part of your search strategy (e.g. only find human studies or only find RCTs). For more information see Methodological search filters below.

Methodological Search Filters

Methodological search filters are search terms/strategies to identify a topic or aspect (e.g. study type, age group). They are "tried and tested" strategies intended for repeated use. If there is a relevant study type filter available, add it to your search.

Sources of filters are:

Useful articles for observational studies:

Limit to English

Limiting study inclusion on the basis of language of publication introduces language bias. Both Cochrane and the Campbell Collaboration advise not to restrict the searches by language. JBI recently acknowledged that limiting searches to English is common practice in JBI systematic reviews but that this should be reconsidered.

Ovid Databases - Limit to a Specific Date Range

This Ovid tool automatically creates the search syntax for limiting a search to a specific date range for any of the Ovid databases:

This might be useful for an update search.

NOTE!  If you need to update a search, it is worth reading the 6.6 Updating searches chapter in the Cochrane Handbook.

Example

For the example, in Step 1, you may have decided to only include studies that are randomised controlled trials (RCTs). For a systematic review it is not recommended to use the limit options that the databases provide. It is a better option to make this refinement part of the search strategy. According to the Cochrane Handbook, you may like to add the Highly Sensitive Search Strategy filter for identifying RCTs to the search. It is added at the end of the search strategy.

This is the Medline via Ovid format for the Cochrane Highly Sensitive Search Strategy for identifying randomized trials in MEDLINE: sensitivity-maximizing version (2008 revision):

  1  randomized controlled trial.pt.
  2  controlled clinical trial.pt.
  3  randomized.ab.
  4  placebo.ab.
  5  drug therapy.fs.
  6  randomly.ab.
  7  trial.ab.
  8  groups.ab.
  9  1 or 2 or 3 or 4 or 5 or 6 or 7 or 8
10  exp animals/ not humans.sh.
11  9 not 10

From Cochrane Handbook, Technical Supplement to Chapter 4, p60-61, Box 3.c

You can run this search strategy after the final search, which combines all four concepts with AND (search 44 in Medline via Ovid Example)

Note!  This filter outlines the proper exclusion of animal studies in a search (see double negative in line 10 and 11)

This is the PubMed format for the Cochrane Highly Sensitive Search Strategy for identifying randomized trials in MEDLINE: sensitivity-maximizing version (2008 revision):

  #1  randomized controlled trial [pt]
  #2  controlled clinical trial [pt]
  #3  randomized [tiab]
  #4  placebo [tiab]
  #5  drug therapy [sh]
  #6  randomly [tiab]
  #7  trial [tiab]
  #8  groups [tiab]
  #9  #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7 OR #8
#10  animals [mh] NOT humans [mh]
#11  #9 NOT #10

From Cochrane Handbook, Technical Supplement to Chapter 4, p60-61, Box 3.a

You can run this search strategy after the final search, which combines all four concepts with AND (search #49 in Medline via PubMed Example).

Note!  This filter outlines the proper exclusion of animal studies in a search (see double negative in line #10 and #11)

Limit to Humans

If you would like to limit your search to Human studies only, please do not use the Human filters provided by the databases. It is best practice to identify animal-only studies first, and then exclude those from the search results (double negative). See a selection of search strategies below:

Medline via Ovid

from Cochrane Handbook, Technical Supplement to Chapter 4 (p62):

not (exp animals/ not humans.sh.)

Medline via PubMed

from Cochrane Handbook, Technical Supplement to Chapter 4 (p61):

NOT (animals [mh] NOT humans [mh])

Embase via Ovid

from Embase: Excerpta Medica Database Guide - Limits: Humans only (removes records about animals):

not ((exp animal/ or exp invertebrate/ or nonhuman/ or animal experiment/ or animal tissue/ or animal model/ or exp plant/ or exp fungus/) not (exp human/ or human tissue/))

CINAHL via EBSCOhost

from Cochrane Handbook, Technical Supplement to Chapter 4 (p66):

NOT (((MH "Animals+") OR (MH "Animal Studies") OR (TI "animal model*")) NOT (MH "human"))

Scopus

Scopus includes MeSH and Emtree terms from Medline and Embase records so you could adapt Medline's and Embase's Limit to Humans strategy:

AND NOT ((INDEXTERMS(animals OR animal)) AND NOT (INDEXTERMS(humans OR human)))

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