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EPIB 629 Knowledge Synthesis

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. Please remember to cite the filters in your work as well, and to note adaptations if applicable.

CINAHL (EBSCOhost) filter/hedge for randomized controlled trials within CINAHL Plus with Full Text:

TX allocat* random* OR (MH "Quantitative Studies") OR (MH "Placebos") OR TX placebo* OR TX random* allocat* OR (MH "Random Assignment") OR TX randomi* control* trial* OR  TX ( (singl* N1 blind*) or (singl* N1 mask*) ) OR TX ( (doubl* N1 blind*) or (doubl* N1 mask*) ) OR  TX ( (tripl* N1 blind*) or (tripl* N1 mask*) ) OR  TX ( (trebl* N1 blind*) or (trebl* N1 mask*) ) OR (TX clinic* N1 trial*) OR PT Clinical trial OR (MH "Clinical Trials+")

Source: Scottish Intercollegiate Guidelines Network

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

(MH randomized controlled trials OR MH double-blind studies OR MH single-blind studies OR MH random assignment OR MH pretest-posttest design OR MH cluster sample OR TI (randomised OR randomized) OR AB (random*) OR TI (trial) OR (MH (sample size) AND AB (assigned OR allocated OR control)) OR MH (placebos) OR PT (randomized controlled trial) OR AB (control W5 group) OR MH (crossover design) OR MH (comparative studies) OR AB (cluster W3 RCT)) NOT ((MH animals+ OR MH animal studies OR TI (animal model*)) NOT MH human)

Source: Glanville J, Dooley G, Wisniewski S, Foxlee R, Noel‐Storr A. Development of a search filter to identify reports of controlled clinical trials within CINAHL Plus. Health Information & Libraries Journal. 2019 Mar;36(1):73-90.

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


Please note: As mentioned in the Cochrane Technical Supplement to Chapter 4, this filter was originally developed based on the MEDLINE-indexed segment of the database. You may wish to add free-text terms (textwords/keywords), or alter the terms used to increase sensitivity, e.g., instead of randomized.ab. or randomised.ab. or randomly.ab., try random*.ti,ab,kf.

Despite the original context of its development, the filter has been shown to have high sensitivity (Glanville J, Kotas E, Featherstone R, Dooley G. Which are the most sensitive search filters to identify randomized controlled trials in MEDLINE? J Med Libr Assoc. 2020;108(4):556-63.)  

The search filter also contains the floating subheading "drug therapy.fs" which may be irrelevant depending on the topic of the review. Finally, the filter is designed to remove studies indexed as being only about non-human animals, so this would need to be modified when necessary.

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. 

Tools for developing a search strategy

These text mining tools can help you identify MeSH terms (subject headings in MEDLINE) related to a concept that you are including in your search strategy. It may be the case that you will have to use a combination of subject headings to capture a single concept.

Great tool for checking if brackets in single line searches are properly balanced

Enter the PubMed ID numbers of known relevant articles and create an HTML or Excel file indicating the MeSH headings used to index those articles.​

Harvey Cushing/John Hay Whitney Medical Library [Internet]. New Haven (CT): Yale Library; [cited 2021 Jan 15]. [Video], Yale MeSH Analyzer; [reviewed 2021 Jan 15, cited 2021 Jan 15]; [7 min., 39 sec]. Available from:

Enter a block of text and MeSH On Demand returns a list of MeSH Terms relevant to your text.

Have you found a line-by-line search strategy for an Ovid database that you would like to re-execute without copying and pasting each line into the search history? Try the Ovid Search History Launcher (if off campus, be sure to log in to McGill VPN beforehand)

  • Try copying and pasting the line-by-line strategy into a Word document > In Word, select all > Remove "numbering"
  • Copy this edited version and paste it into the Ovid Search History Launcher
  • Select Ovid MEDLINE ALL [medall] if searching MEDLINE and run the search

Useful for entering a high precision search on your topic or the PMIDs (PubMed unique identifiers) of articles that are relevant to your topic: PubReminer ranks the indexing terms (e.g., MeSH) or words that are most commonly associated with that set of records

See also: Text mining for searching and screening the literature

  • Look at the search strategies of other relevant knowledge syntheses

Look for syntheses that are about at least one of your concepts to see how other researchers developed their search strategies. Remember that search strategies are database and platform specific: e.g., an Ovid MEDLINE search strategy has to be built with its own syntax -- even if it uses MeSH -- and thus would have to be translated to PubMed, and vice-versa. Different databases, like Embase and PsycINFO for example, will also use their own subject headings: Be careful when reusing search strategies to make sure they are database and platform appropriate.

  • Check the indexing of relevant articles

If you have already found articles that your search should be picking up, copy and paste the article title into an article database like PubMed to see how it is indexed, if applicable.

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/)

PsycInfo on Ovid SP:

  • NOT ((adolescence 13 17 yrs or childhood birth 12 yrs) not adulthood 18 yrs older).ag.


  • 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/)

PsycInfo on OvidSP:

  •  NOT     ((adulthood 18 yrs older) not (adolescence 13 17 yrs or childhood birth 12 yrs) ).ag.


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

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