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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.

Approaching the Search

A systematic review aims to capture as many relevant studies (studies are considered data for systematic reviews) as possible as well as to minimize bias. Searching for data for a systematic review is very different than standard database searching. Instead of looking for a short list of "the most appropriate" citations, you're attempting to cast a very wide net in hopes of finding as much relevant data as possible. 

Use the PICO framework from the Frame Your Question section to build robust sets of synonyms and controlled vocabularies for your PICO elements. Below is a simplified version of this process for the question "Which is better for treating fever in children, acetaminophen or ibuprofen?" using PubMed.

Concepts Controlled Vocabulary Keywords Search Strategy
P Children "Child"[Mesh], "Child, Preschool"[Mesh], "Adolescent"[Mesh], "Infant"[Mesh], "Infant, Newborn"[Mesh], "Pediatrics"[Mesh] child, children, pediatrics, infant, toddler "Child"[Mesh] OR "Child, Preschool"[Mesh] OR "Adolescent"[Mesh] OR "Infant"[Mesh] OR "Infant, Newborn"[Mesh] OR child* OR pediatric* OR infant OR toddler
I Acetaminophen "Acetaminophen"[Mesh] Panadol, Tylenol, Acetaminophen "Acetaminophen"[Mesh] OR Panadol OR Tylenol OR Acetaminophen
C Ibuprofen "Ibuprofen"[Mesh] Advil, Motrin, ibuprofen "Ibuprofen"[Mesh] OR Advil OR Motrin OR ibuprofen
O Reduced Fever "Fever"[Mesh] fever, hyperpyrexia, pyrexia "Fever"[Mesh] OR fever OR hyperpyrexia OR pyrexia

The final PubMed search strategy will look like this: 

("Child"[Mesh] OR "Child, Preschool"[Mesh] OR "Adolescent"[Mesh] OR "Infant"[Mesh] OR "Infant, Newborn"[Mesh] OR child* OR pediatric* OR infant OR toddler) AND ("Acetaminophen"[Mesh] OR Panadol OR Tylenol OR Acetaminophen) AND ("Ibuprofen"[Mesh] OR Advil OR Motrin OR ibuprofen) AND ("Fever"[Mesh] OR fever OR hyperpyrexia OR pyrexia)

Recommended Databases

At the very minimum, at least the three databases listed below in "Recommended Databases" should be used. 

Subject Specific Databases: Based on your topic, you may want to search subject specific databases

Search Hedges for Common Subject Areas

  • 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 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/)))
  • 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 humans.sh.)
  • 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])

Search Hedges to selectively remove content

  • 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.

https://docs.google.com/document/d/1mpqZsuCPCbCxmFUf5ndjIUaCCbyu-UmMyWlGGydVgwE/edit

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.

http://guides.library.ualberta.ca/ld.php?content_id=14026757

Documenting Your Search Strategy

Every systematic review requires authors document at least one search strategy (though if you're allowed the space, including more strategies makes your review more replicable).  information that should be included is:

  • Database and coverage range - Make sure you indicate both the database and the vendor or platform - for instance, if you used Medline, was that through Ovid, Ebsco, Proquest, PubMed, or some other vendor? If you used Ovid, did you search a section of Medline, or the entire database?
  • Latest Search Date - This is the date you ran the searches. This goes toward replicability as well as currency - if your search was conducted a full year before publication, there may be missed content.
  • Full Electronic Search Strategy - As best as you can, copy and paste the exact strategy directly out of the database. Re-typing invites error. Do not truncate or abbreviate the search strategy, or offer a list of "representative concepts," as that renders the search strategy unreproducible. Include database syntax. For example, in PubMed you may have field tags, parentheses, and other commands (("Neoplasms"[MAJR]) AND ("Heart Lung"[Journal] OR "JAMA"[Journal])) that effect the search results. It is important these are represented in order for someone to reproduce your search.
  • Any limits used (date, language, publication type, etc.).
  • Number of unique records retrieved by searches.
  • Total number of citations retrieved.

Grey Literature

Grey (or gray) literature is loosely described as "anything that is not a journal or a book." This leaves a wide range of resources, from advocacy reports to conference proceedings to government documents to trial registries. The sources you choose to examine will be determined by the subject and nature of your systematic review project.

The value of grey literature is that it allows for inclusion of non-published data. There can be a bias in publication to show positive results, or to show significant effect. However, sometimes experiments result in negative or mixed results. This data is just as valuable, but is not as frequently published, and looking at conference proceedings or trial registries will help your project come closer to truth than only examining published literature. 

It is important to look outside of information published in databases in order to reduce publication bias - which is described both as journals encouraging novel research and discouraging negative results, and authors self-censoring by not submitting negative results for publication. Several manuals including the Cochrane Handbook and PRISMA for systematic review protocol recommend and incorporate the use of grey literature searching.

Sources for grey literature searching

Subjects: Health Sciences