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Systematic Reviews: A How-To Guide

Overview of systematic review steps and resources to assist researchers conducting reviews

About Search Filters

Search filters, sometimes called hedges, are strings of search terms that are used to limit search results. Many databases feature a built-in set of search filters that are commonly used to limit search results by age group, publication type, study type, and more.

When conducting a systematic review, however, there is a possibility that these filters may exclude relevant studies. For this reason, search experts and institutions have developed their own search filters, and many are available online for public use.

Example PubMed Search Filters

Randomized Controlled Trials

From the Cochrane Handbook, Section 6.4.11, Box 6.4.a:

(((((((((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])) 

From Glanville, J. M., Lefebvre, C., Miles, J. N. V., & Camosso-Stefinovic, J. (2006). How to identify randomized controlled trials in MEDLINE: ten years on. Journal of the Medical Library Association94(2), 130–136.:

(((((((clinical trial[pt]) OR randomized[tiab]) OR placebo[tiab]) OR clinical trials[mh]) OR randomly[tiab]) OR trial[ti])) NOT ((animals[mh]) NOT (animals[mh] AND humans[mh])) 

Qualitative Studies

From University of Texas School of Public Health:

“interviews as topic”[Mesh:noexp] OR “focus groups”[Mesh:noexp] OR narration[Mesh:noexp] OR qualitative research[Mesh:noexp] OR (((“semi-structured”[TIAB] OR semistructured[TIAB] OR unstructured[TIAB] OR structured[TIAB] OR informal[TIAB] OR “in-depth”[TIAB] OR indepth[TIAB] OR “face-to-face”[TIAB] OR guide[TIAB] OR guides[TIAB]) AND (interview*[TIAB] OR discussion*[TIAB] OR questionnaire*[TIAB])) OR (“focus group”[TIAB] OR “focus groups”[TIAB] OR qualitative[TIAB] OR ethnograph*[TIAB] OR fieldwork[TIAB] OR “field work”[TIAB] OR “key informant”[TIAB]))

Systematic Reviews

Adapted from SIGN:

((((((((((("Meta-Analysis as Topic"[Mesh]) OR meta analy*[tw]) OR metaanaly*[tw]) OR Meta-Analysis[pt]) OR (((systematic AND (review* OR overview*)) AND tw))) OR "Review Literature as Topic"[Mesh])) OR ((((((((cochrane[tiab]) OR embase[tiab]) OR ((psychlit OR psyclit[tiab]))) OR ((psychinfo OR psycinfo[tiab]))) OR ((cinahl OR cinhal[tiab]))) OR science citation index[tiab]) OR bids[tiab]) OR cancerlit[tiab])) OR (((((reference list*[tiab]) OR bibliograph*[tiab]) OR hand-search*[tiab]) OR relevant journals[tiab]) OR manual search*[tiab])) OR ((((selection criteria[tiab]) OR data extraction[tiab])) AND "Review"[pt]))) NOT (((("Comment"[pt]) OR "Letter"[pt]) OR "Editorial"[pt]) OR (("Animals"[Mesh]) NOT (("Animals"[Mesh] AND "Humans"[Mesh])))) 

Example CINAHL Search Filters

Randomized Controlled Trials

From University of Alberta:

( (MH "Random Assignment") or (MH "Random Sample+") or (MH "Crossover Design") or (MH "Clinical Trials+") or (MH "Comparative Studies") or (MH "Control (Research)+") or (MH "Control Group") or (MH "Factorial Design") or (MH "Quasi-Experimental Studies+") or (MH "Placebos") or (MH "Meta Analysis") or (MH "Sample Size") or (MH "Research, Nursing") or (MH "Research Question") or (MH "Research Methodology+") or (MH "Evaluation Research+") or (MH "Concurrent Prospective Studies") or (MH "Prospective Studies") or (MH "Nursing Practice, Research-Based") or (MH "Solomon Four-Group Design") or (MH "One-Shot Case Study") or (MH "Pretest-Posttest Design+") or (MH "Static Group Comparison") or (MH "Study Design") or (MH "Clinical Research+") ) or ( clinical nursing research or random* or cross?over or placebo* or control* or factorial or sham* or meta?analy* or systematic review* or blind* or mask* or trial* ) 

Qualitative Studies

From the University of Washington:

(MH "cluster sample+") or TX life experiences or TX human science or TX discourse* analysis or TX narrative analysis or TX lived experience* or TX field research or TX field studies or TX field study or TX giorgi* or TX husserl* or TX merleau ponty* or TX van kaam* or TX van manen* or TX spiegelberg* or TX colaizzi* or TX heidegger* or TX participant observ* or TX data saturat* or TX semiotics or TX heuristic or TX hermeneutic* or TX etic or TX emic or TX focus group* or TX purpos* sampl* or TX constant comparison or TX constant comparative or TX grounded research or TX grounded studies or TX grounded study or TX grounded theor* or TX phenomenol* or TX ethnon* or TX qualitative or (MH "ethnological research") or (MH "ethnography") or (MH "phenomenology") or (MH "focus groups") or (MH "discourse analysis") or (MH "theoretical sample") or (MH "field studies") or (MH "constant comparative method") or (MH "thematic analysis") or (MH "content analysis") or (MH "observational methods+") or (MH "purposive sample") or (MH "qualitative validity+") or (MH "grounded theory") or (MH “action research”) or (MH “naturalistic inquiry”) or (MH "ethnonursing research") or (MH "phenomenological research") or (MH "ethnographic research") or (MH "qualitative studies") or (MH "Interviews+") or (MH "Narratives") or (MH "Videorecording+") or (MH "Audiorecording") or (MH "Historical Records") 

Systematic Reviews

From University of Texas School of Public Health:

(TI (systematic* n3 review*)) or (AB (systematic* n3 review*)) or (TI (systematic* n3 bibliographic*)) or (AB (systematic* n3 bibliographic*)) or (TI (systematic* n3 literature)) or (AB (systematic* n3 literature)) or (TI (comprehensive* n3 literature)) or (AB (comprehensive* n3 literature)) or (TI (comprehensive* n3 bibliographic*)) or (AB (comprehensive* n3 bibliographic*)) or (TI (integrative n3 review)) or (AB (integrative n3 review)) or (JN “Cochrane Database of Systematic Reviews”) or (TI (information n2 synthesis)) or (TI (data n2 synthesis)) or (AB (information n2 synthesis)) or (AB (data n2 synthesis)) or (TI (data n2 extract*)) or (AB (data n2 extract*)) or (TI (medline or pubmed or psyclit or cinahl or (psycinfo not “psycinfo database”) or “web of science” or scopus or embase)) or (AB (medline or pubmed or psyclit or cinahl or (psycinfo not “psycinfo database”) or “web of science” or scopus or embase)) or (MH “Systematic Review”) or (MH “Meta Analysis”) or (TI (meta-analy* or metaanaly*)) or (AB (meta-analy* or metaanaly*))

Example Embase Search Filters

Randomized Controlled Trials

Adapted from the Cochrane Handbook by the Cochrane Occupational Health and Safety Group:

'crossover procedure':de OR 'double-blind procedure':de OR 'randomized controlled trial':de OR  'single-blind procedure':de OR (random* OR  factorial* OR crossover* OR cross NEXT/1 over* OR placebo* OR doubl* NEAR/1 blind* OR singl* NEAR/1 blind* OR assign* OR allocat* OR volunteer*):de,ab,ti

Adapted from SIGN by the Cochrane Occupational Health and Safety Group:

'clinical trial'/de OR 'randomized controlled trial'/de OR 'randomization'/de OR 'single blind procedure'/de OR 'double blind procedure'/de OR 'crossover procedure'/de OR 'placebo'/de OR 'prospective study'/de OR 'randomi?ed controlled' NEXT/1 trial* OR rct OR 'randomly allocated' OR 'allocated randomly' OR 'random allocation' OR allocated NEAR/2 random OR single NEXT/1 blind* OR double NEXT/1 blind* OR (treble OR triple) NEAR/1 blind* OR placebo*

Qualitative Studies

Adapted from McMaster HIRU:

interview:de,ab,ti OR 'health care organization'/exp OR experiences:de,ab,ti