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EPIB 619 Systematic Reviews & Meta-Analyses

Search filters or hedges

Search filters, sometimes also called hedges or search blocks, are search strategies that usually include a series of pre-elaborated free-text terms/textwords/words/phrases plus subject headings for a given concept, idea, or study design; these search strategies have already been developed to find literature on the concept/idea/study design of interest within a particular database/platform (e.g., for the MEDLINE database on the Ovid platform). They may or may not have been validated for their sensitivity/specificity/precision, but when available, they are a useful tool to take advantage of work that others have already done to identify terms to find literature on a given concept.

If reusing search filters that others have developed, please cite or acknowledge them.

Useful sources of general search filters

Additional/more specific filters not listed above or suggested at McGill

In addition to using search filters or hedges, you may find it useful to consult other systematic reviews or knowledge syntheses related to at least one of the concepts of your search, to see how they developed the search strategy for the concept of interest. One trick, for example, is to search the Cochrane Library by restricting the term of interest to the title field in the record, and then looking at the search strategy in the full-text, as it is often well documented in Cochrane reviews. Ideally, you should check a few reviews given the quality of the searches can be quite heterogeneous.

RCT search filters for MEDLINE on Ovid, EMBASE on Ovid, and PubMed

RCT search filters/hedges

Use these pre-formulated search strategies (database-specific) to limit your results to randomized controlled trials or controlled clinical trials, depending on the strategy available. To do so, just copy and paste the appropriate strategy into the database search box and add it to your search with the Boolean operator AND.


CINAHL (EBSCOhost) filter/hedge for controlled clinical trials:


Cochrane Highly Sensitive Search Strategy for identifying controlled trials in Embase

(Randomized controlled trial/ or Controlled clinical study/ or random$.ti,ab. or randomization/ or intermethod comparison/ or placebo.ti,ab. or (compare or compared or comparison).ti. or ((evaluated or evaluate or evaluating or assessed or assess) and (compare or compared or comparing or comparison)).ab. or (open adj label).ti,ab. or ((double or single or doubly or singly) adj (blind or blinded or blindly)).ti,ab. or double blind procedure/ or parallel group$1.ti,ab. or (crossover or cross over).ti,ab. or ((assign$ or match or matched or allocation) adj5 (alternate or group$1 or intervention$1 or patient$1 or subject$1 or participant$1)).ti,ab. or (assigned or allocated).ti,ab. or (controlled adj7 (study or design or trial)).ti,ab. or (volunteer or volunteers).ti,ab. or human experiment/ or trial.ti.) not (((random$ adj sampl$ adj7 ("cross section$" or questionnaire$1 or survey$ or database$1)).ti,ab. not (comparative study/ or controlled study/ or randomi?ed controlled.ti,ab. or randomly assigned.ti,ab.)) or (Cross-sectional study/ not (randomized controlled trial/ or controlled clinical study/ or controlled study/ or randomi?ed controlled.ti,ab. or control group$1.ti,ab.)) or (((case adj control$) and random$) not randomi?ed controlled).ti,ab. or (Systematic review not (trial or study)).ti. or (nonrandom$ not random$).ti,ab. or "Random field$".ti,ab. or (random cluster adj3 sampl$).ti,ab. or ((review.ab. and not trial.ti.) or ("we searched".ab. and (review.ti. or or "update review".ab. or (databases adj4 searched).ab. or ((rat or rats or mouse or mice or swine or porcine or murine or sheep or lambs or pigs or piglets or rabbit or rabbits or cat or cats or dog or dogs or cattle or bovine or monkey or monkeys or trout or marmoset$1).ti. and animal experiment/) or (Animal experiment/ not (human experiment/ or human/)))

Source: Box 3.e. Technical Supplement to Chapter 4: Searching for and Selecting StudiesCochrane Handbook for Systematic Reviews of Interventions Version 6. 


MEDLINE (Ovid) highly sensitive filter/hedge for RCTs, modified with addition of randomised.ab.

((randomized controlled trial or controlled clinical trial).pt. or randomized.ab. or randomised.ab. or placebo.ab. or drug therapy.fs. or randomly.ab. or trial.ab. or groups.ab.) not (exp animals/ not

Source: Box 3.c., Technical Supplement to Chapter 4: Searching for and Selecting StudiesCochrane Handbook for Systematic Reviews of Interventions Version 6. 


PubMed highly sensitive filter/hedge for RCTs, modified with addition of randomised[tiab]:

((randomized controlled trial[pt]) OR (controlled clinical trial[pt]) OR (randomized[tiab] OR randomised[tiab]) OR (placebo[tiab]) OR (drug therapy[sh]) OR (randomly[tiab]) OR (trial[tiab]) OR (groups[tiab])) NOT (animals[mh] NOT humans[mh])

Source: Box 3.b., Technical Supplement to Chapter 4: Searching for and Selecting StudiesCochrane Handbook for Systematic Reviews of Interventions Version 6. 

Exclusion filters to selectively remove records

Use NOT statements with great care. We do not advise excluding records based on keyword searches.

Please note that these exclusion filters are database and platform-dependent (e.g., the exclusion filter for MEDLINE on PubMed will be different from the exclusion filter for MEDLINE on OvidSP because the platforms are searched differently).

To remove studies indexed as animals only


  • not (exp animals/ not


  • NOT ("animals"[mesh] NOT "humans"[mesh])

Embase on OvidSP:

To remove studies indexed as child only


  • not ((exp infant/ or exp child/ or adolescent/) not (exp adult/))


  • NOT (("infant"[mesh] OR "child"[mesh] OR "adolescent"[mesh]) NOT ("adult"[mesh])

Embase on OvidSP:

  • not (exp juvenile/ not exp adult/)


  • NOT ( (MH "Child+") or (MH "Adolescence") ) NOT (MH "Adult+") 

To remove studies indexed as adult only


  • not (exp adult/ not (exp infant/ or exp child/ or adolescent/))


  • NOT ("adult"[mesh] NOT ("infant"[mesh] OR "child"[mesh] OR "adolescent"[mesh]))

Embase on OvidSP:

  • not (exp adult/ not exp juvenile/)


  • Not (MH "Adult+" not (MH "Child+") or (MH "Adolescence"))

Liaison Librarian

Genevieve Gore's picture
Genevieve Gore
Liaison Librarian, Schulich Library of Physical Sciences, Life Sciences, and Engineering
On sabbatical from Jan 1 to Jun 30, 2021
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