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Systematic Reviews

What are search filters

Search filters are search strategies that have been devised and tested to filter the results of your search from large, general purpose databases including MEDLINE, EMBASE, and PsycINFO.   It is also known as "hedges" used to limit search results by 

  • a specific clinical study category 
  • systematic reviews, meta-analyses, reviews of clinical trials, evidence-based medicine
  • age group

You may find the built-in search filters provided by the specific databases.  For systematic review, we would recommend you to use a validated search filter if there is a need to apply it.  If you reuse search filters that others have developed, you should acknowledge the sources that you cite.  Please refer to the list of resources for search filters in the next section to explore further. 

Search filters resources

InterTASC ISSG Search Filter Resource

Cochrane Handbook See Part 2 - Section 6.4.11: Search Filters

Pubmed Clinical Queries  Enter your search term and your results will be automatically categorised into Clinical Study categories, Systematic Reviews and Medical Genetics. 

Scottish Intercollegiate Guidelines Network (SIGN) Search Filters

Type of search filters

The Covid-19 search filter was developed by NUS Medical Library (not validated) .  Please feel free to adapt the search strategy to meet your research needs. 

Cochrane highly sensitive search strategies for identifying randomized trials in PubMed 

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


Cochrane Highly Sensitive Search Strategy for identifying randomized trials in MEDLINE(OVID) 

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

Refer to the Cochrane Handbook for details.

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

(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.

Searching Scopus for "Randomised Control Trials" .


( INDEXTERMS ( "clinical trials" OR "clinical trials as a topic" OR "randomized controlled trial" OR "Randomized Controlled Trials as Topic" OR "controlled clinical trial" OR "Controlled Clinical Trials" OR "random allocation" OR "Double-Blind Method" OR "Single-Blind Method" OR "Cross-Over Studies" OR "Placebos" OR "multicenter study" OR "double blind procedure" OR "single blind procedure" OR "crossover procedure" OR "clinical trial" OR "controlled study" OR "randomization" OR "placebo" ) ) OR ( TITLE-ABS-KEY ( ( "clinical trials" OR "clinical trials as a topic" OR "randomized controlled trial" OR "Randomized Controlled Trials as Topic" OR "controlled clinical trial" OR "Controlled Clinical Trials as Topic" OR "random allocation" OR "randomly allocated" OR "allocated randomly" OR "Double-Blind Method" OR "Single-Blind Method" OR "Cross-Over Studies" OR "Placebos" OR "cross-over trial" OR "single blind" OR "double blind" OR "factorial design" OR "factorial trial" ) ) ) OR ( TITLE-ABS ( clinical trial* OR trial* OR rct* OR random* OR blind* ) )

This filter was developed by NUS Medical Library (not validated) using MESH and EMTREE terms as Index terms and Keywords.

Useful to search in Scopus for RCTs.

These are the qualitative research filters that you can try to identify qualitative studies as appropriate. 

1) Health Services Research (HSR) PubMed Queries 

2) Please click this link  to explore the use of other qualitative filters.