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.
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.
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.
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+")
(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.
(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 review.pt.) not trial.ti.) or ("we searched".ab. and (review.ti. or review.pt.)) 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 Studies. Cochrane Handbook for Systematic Reviews of Interventions Version 6.
((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 humans.sh.)
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 Studies. Cochrane Handbook for Systematic Reviews of Interventions Version 6.
((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 Studies. Cochrane Handbook for Systematic Reviews of Interventions Version 6.
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).
MEDLINE on OvidSP:
Embase on OvidSP:
MEDLINE on OvidSP:
Embase on OvidSP:
PsycInfo on Ovid SP:
MEDLINE on OvidSP:
Embase on OvidSP:
PsycInfo on OvidSP: