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Systematic Reviews

This guide explains the principles of systematic reviews and offers advice on getting started with your systematic literature search.

What is a search filter or hedge?

Search filters or hedges are search strategies that include a series of pre-elaborated free text terms/text words/phrases and subject headings for a given concept, idea, or study design. Though the terms "search filters" and "hedges" may be used interchangeably, search filters refer to methods that refine static concepts, such as study design, whereas hedges deal with subject materials.

Useful sources of general search filters

Tools for developing a search strategy

Exclusion filters to selectively remove records

    • Embase: 'africa'/exp OR 'south and central america'/exp OR 'central america'/exp OR 'caribbean'/exp OR 'south america'/exp OR 'mexico'/exp OR 'asia'/exp OR 'borneo'/exp OR 'brunei darussalam'/exp OR 'cambodia'/exp OR 'southeast asia'/exp OR 'indonesia'/exp OR 'laos'/exp OR 'malaysia'/exp OR 'myanmar'/exp OR 'philippines'/exp OR 'thailand'/exp OR 'timor-leste'/exp OR 'viet nam'/exp OR 'mongolia'/exp OR 'albania'/exp OR 'baltic states'/exp OR 'bosnia and herzegovina'/exp OR 'bulgaria'/exp OR 'kosovo'/exp OR 'montenegro (republic)'/exp OR 'belarus'/exp OR 'republic of north macedonia'/exp OR 'serbia'/exp OR 'ukraine'/exp OR 'ussr'/exp OR ((afghanistan:ti,ab,kw OR angola:ti,ab,kw OR albania:ti,ab,kw OR argentina:ti,ab,kw OR armenia:ti,ab,kw OR 'american samoa':ti,ab,kw OR azerbaijan:ti,ab,kw OR burundi:ti,ab,kw OR benin:ti,ab,kw OR burkina:ti,ab,kw) AND faso:ti,ab,kw) OR bangladesh:ti,ab,kw OR bulgaria:ti,ab,kw OR bosnia:ti,ab,kw OR herzegovina:ti,ab,kw OR belarus:ti,ab,kw OR belize:ti,ab,kw OR bolivia:ti,ab,kw OR brazil:ti,ab,kw OR bhutan:ti,ab,kw OR botswana:ti,ab,kw OR 'central african republic':ti,ab,kw OR china:ti,ab,kw OR 'ivory coast':ti,ab,kw OR ivoire:ti,ab,kw OR cameroon:ti,ab,kw OR congo:ti,ab,kw OR colombia:ti,ab,kw OR comoros:ti,ab,kw OR 'cabo verde':ti,ab,kw OR 'costa rica':ti,ab,kw OR cuba:ti,ab,kw OR djibouti:ti,ab,kw OR dominica:ti,ab,kw OR 'dominican republic':ti,ab,kw OR algeria:ti,ab,kw OR ecuador:ti,ab,kw OR egypt:ti,ab,kw OR eritrea:ti,ab,kw OR ethiopia:ti,ab,kw OR fiji:ti,ab,kw OR micronesia:ti,ab,kw OR gabon:ti,ab,kw OR georgia:ti,ab,kw OR ghana:ti,ab,kw OR guinea:ti,ab,kw OR gambia:ti,ab,kw OR grenada:ti,ab,kw OR guatemala:ti,ab,kw OR guyana:ti,ab,kw OR honduras:ti,ab,kw OR haiti:ti,ab,kw OR indonesia:ti,ab,kw OR india:ti,ab,kw OR iran:ti,ab,kw OR iraq:ti,ab,kw OR jamaica:ti,ab,kw OR jordan:ti,ab,kw OR kazakhstan:ti,ab,kw OR kenya:ti,ab,kw OR kyrgyz*:ti,ab,kw OR cambodia:ti,ab,kw OR kiribati:ti,ab,kw OR lao:ti,ab,kw OR laos:ti,ab,kw OR lebanon:ti,ab,kw OR liberia:ti,ab,kw OR libya:ti,ab,kw OR lucia:ti,ab,kw OR 'sri lanka':ti,ab,kw OR lesotho:ti,ab,kw OR morocco:ti,ab,kw OR moldova:ti,ab,kw OR madagascar:ti,ab,kw OR maldives:ti,ab,kw OR mexico:ti,ab,kw OR 'marshall islands':ti,ab,kw OR macedonia:ti,ab,kw OR mali:ti,ab,kw OR myanmar:ti,ab,kw OR montenegro:ti,ab,kw OR mongolia:ti,ab,kw OR mozambique:ti,ab,kw OR mauritania:ti,ab,kw OR malawi:ti,ab,kw OR malaysia:ti,ab,kw OR namibia:ti,ab,kw OR niger:ti,ab,kw OR nigeria:ti,ab,kw OR nicaragua:ti,ab,kw OR nepal:ti,ab,kw OR pakistan:ti,ab,kw OR peru:ti,ab,kw OR philippines:ti,ab,kw OR 'papua new guinea':ti,ab,kw OR 'north korea':ti,ab,kw OR dprk:ti,ab,kw OR paraguay:ti,ab,kw OR 'west bank':ti,ab,kw OR gaza:ti,ab,kw OR rwanda:ti,ab,kw OR sudan:ti,ab,kw OR senegal:ti,ab,kw OR 'solomon islands':ti,ab,kw OR 'sierra leone':ti,ab,kw OR 'el salvador':ti,ab,kw OR somalia:ti,ab,kw OR serbia:ti,ab,kw OR 'sao tome':ti,ab,kw OR principe:ti,ab,kw OR suriname:ti,ab,kw OR eswatini:ti,ab,kw OR syria*:ti,ab,kw OR chad:ti,ab,kw OR togo:ti,ab,kw OR thailand:ti,ab,kw OR tajikistan:ti,ab,kw OR turkmenistan:ti,ab,kw OR timor:ti,ab,kw OR tonga:ti,ab,kw OR tunisia:ti,ab,kw OR turkey:ti,ab,kw OR tuvalu:ti,ab,kw OR tanzania:ti,ab,kw OR uganda:ti,ab,kw OR ukraine:ti,ab,kw OR uzbekistan:ti,ab,kw OR grenadines:ti,ab,kw OR vietnam:ti,ab,kw OR vanuatu:ti,ab,kw OR samoa:ti,ab,kw OR kosovo:ti,ab,kw OR yemen:ti,ab,kw OR 'south africa':ti,ab,kw OR zambia:ti,ab,kw OR zimbabwe:ti,ab,kw
    • Medline: exp "Africa"/ or "Latin America"/ or "Central America"/ or "Caribbean Region"/ or "South America"/ or "Mexico"/ or "Asia, Central"/ or "Asia, Northern"/ or "Borneo"/ or "Brunei"/ or "Cambodia"/ or "Indochina"/ or "Indonesia"/ or "Laos"/ or "Malaysia"/ or "Mekong Valley"/ or "Myanmar"/ or "Philippines"/ or "Thailand"/ or "Timor-Leste"/ or "Vietnam"/ or "Asia, Western"/ or "Mongolia"/ or "Albania"/ or "Baltic States"/ or "Bosnia and Herzegovina"/ or "Bulgaria"/ or "Kosovo"/ or "Montenegro"/ or "Republic of Belarus"/ or "Republic of North Macedonia"/ or "Serbia"/ or "Ukraine"/ or "Transcaucasia"/ OR (Afghanistan or Angola or Albania or Argentina or Armenia or "American Samoa" or Azerbaijan or Burundi or Benin or Burkina Faso or Bangladesh or Bulgaria or Bosnia or Herzegovina or Belarus or Belize or Bolivia or Brazil or Bhutan or Botswana or "Central African Republic" or China or "Ivory Coast" or Ivoire or Cameroon or Congo or Colombia or Comoros or "Cabo Verde" or "Costa Rica" or Cuba or Djibouti or Dominica or "Dominican Republic" or Algeria or Ecuador or Egypt or Eritrea or Ethiopia or Fiji or Micronesia or Gabon or Georgia or Ghana or Guinea or Gambia or Grenada or Guatemala or Guyana or Honduras or Haiti or Indonesia or India or Iran or Iraq or Jamaica or Jordan or Kazakhstan or Kenya or Kyrgyz* or Cambodia or Kiribati or Lao or Laos or Lebanon or Liberia or Libya or Lucia or "Sri Lanka" or Lesotho or Morocco or Moldova or Madagascar or Maldives or Mexico or "Marshall Islands" or Macedonia or Mali or Myanmar or Montenegro or Mongolia or Mozambique or Mauritania or Malawi or Malaysia or Namibia or Niger or Nigeria or Nicaragua or Nepal or Pakistan or Peru or Philippines or "Papua New Guinea" or "North Korea" or DPRK or Paraguay or "West Bank" or Gaza or Rwanda or Sudan or Senegal or "Solomon Islands" or "Sierra Leone" or "El Salvador" or Somalia or Serbia or "Sao Tome" or Principe or Suriname or Eswatini or Syria* or Chad or Togo or Thailand or Tajikistan or Turkmenistan or Timor or Tonga or Tunisia or Turkey or Tuvalu or Tanzania or Uganda or Ukraine or Uzbekistan or Grenadines or Vietnam or Vanuatu or Samoa or Kosovo or Yemen or "South Africa" or Zambia or Zimbabwe
    • CINAHL (Ebscohost): See 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 (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/)))
    • MEDLINE (Ovid) Highly Sensitive: ((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
    • PubMed Highly Sensitive: ((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])

Hedges for common subject areas

    • Medline: not (exp animals/ not
    • PubMed: NOT ("animals"[mesh] NOT "humans"[mesh])
    • Embase: not ((exp animal/ or animal experiment/ or nonhuman/) not (exp human/ or human experiment/)) [Adapted from]
    • Medline: not ((exp infant/ or exp child/ or adolescent/) not (exp adult/))
    • PubMed: NOT (("infant"[mesh] OR "child"[mesh] OR "adolescent"[mesh]) NOT ("adult"[mesh])
    • Embase: not (exp juvenile/ not exp adult/)
    • CINAHL: NOT ( (MH "Child+") or (MH "Adolescence") ) NOT (MH "Adult+")
    • Medline: not (exp adult/ not (exp infant/ or exp child/ or adolescent/))
    • PubMed: NOT ("adult"[mesh] NOT ("infant"[mesh] OR "child"[mesh] OR "adolescent"[mesh]))
    • Embase: not (exp adult/ not exp juvenile/)
    • CINAHL: Not (MH "Adult+" not (MH "Child+") or (MH "Adolescence"))

Campbell, Sandy. Filter to Retrieve Studies Related to Animals from the OVID Medline Database. John W. Scott Health Sciences Library, University of Alberta. Rev. February 26, 2020.

Campbell, Sandy. Filter to Retrieve Studies Related to Watchful Waiting from the Ovid MEDLINE Database. John W. Scott Health Sciences Library, University of Alberta. Rev. November 26, 2015.