Skip to main content

Systematic Reviews

Scoping the Topic

Initial searches are scoping exercises, giving an overview of the topic, placing your work in the context of already published studies and working out:

  • if it has already been carried out
  • the size of the published literature
  • gaps in the literature
  • types of studies and research designs
  • geographical spread of publications

Initial searches also identify: 

  • the relevance of various contexts to your topic
  • concepts that appear in the results which are peripheral to your topic
  • concepts within your topic which are missing from the results

At this stage, skim the results to identify the above.  Look at titles, abstracts, subject headings.  Initial search strategies will be amended for relevancy and accuracy following feedback from this appraisal of results.

Database search process flow chart

Concepts

Break your topic down into constituent concepts.  Depending on your topic, the PICO format may be used to identify the concepts:

  • Patient / Population / Problem
  • Intervention: cause, prognostic factor, treatment
  • Comparison /control (if appropriate)
  • Outcome

Identifying Search Terms

Initial searches explore various keywords and subject headings and combinations of both. 

Using key papers already known to you:

  • Find the record on a database such as PubMed
  • What words/phrases (keywords) does the author use in the title and abstract?
  • What subject headings are used on the record?

Search a relevant database and narrow your words to the titles of the articles.  Look closely at the records:

  • What words/phrases (keywords) does the author use in the title and abstract?
  • What subject headings are used on the record?
  • Are there different subject headings to describe the same concept?  Do you need to use several subject headings in your strategy?

Adapting the search strategy from a similar study:

  • Be critical
  • Amend for your topic

Putting Search Terms Together

You are ideally looking for a combination of keywords and subject headings to describe each aspect of the topic.  Use OR to combine the words and subject headings which describe each aspect.

Finally combine the aspects together with AND.

To help clarify the logic of the search, it may help to consider it schematically.  Identify and group the main keywords and subject headings.

This is a search derived from a systematic review entitled:  “Systematic review of risk prediction models for falls after stroke.”

Venn Diagram 

Use the thesaurus of subject headings within the various databases to identify relevant headings. 

For example, in PubMed Medline, select the MeSH database to find additional relevant Medical Subject Headings to add to the keywords.

MESH example

 

‘Systematic review of risk prediction models for falls after stroke’[1]

In the published review, searches were conducted on seven databases (Medline, Embase, CINAHL, PsychINFO, Web of Science, Cochrane Library and SCOPUS.  In accordance with best practice the published review presents all search strings as executed on all databases as supplemental data.  

The table below gives a summary search strategy for this topic for PubMed Medline.
 

Aspect Keywords Subject headings

Stroke / brain trauma

stroke[Title/Abstract] OR poststroke[Title/Abstract] OR hemiplegia[Title/Abstract] OR brain hemorrhage[Title/Abstract] “Cerebrovascular Disorders"[Mesh] OR "Cerebrovascular Trauma"[Mesh] OR "Stroke"[Mesh] OR "Brain Infarction"[Mesh]
  AND  
Falls falls[Title/Abstract] OR falling[Title/Abstract] OR accident[Title/Abstract] OR accidents[Title/Abstract] OR slips[Title/Abstract] OR trips[Title/Abstract] OR tripped[Title/Abstract] OR stumble[Title/Abstract] “Accidental Falls”[Mesh] OR “Accidents”[Mesh]
  AND  
Risk risk[Title/Abstract] OR prediction[Title/Abstract] OR predictive[Title/Abstract] OR score[Title/Abstract] "Risk"[Mesh] OR "Risk Assessment"[Mesh] OR "Risk Management"[Mesh]

Appendix 2  of this guide gives the full versions of this full search for PubMed Medline and EMBASE databases.


[1] Walsh ME, Horgan NF, Walsh CD, et al Systematic review of risk prediction models for falls after stroke J Epidemiol Community Health 2016;70:513-519.

“Topical non-steroidal anti-inflammatory drugs for analgesia in traumatic corneal abrasions’[1]

OBJECTIVES:  To identify and evaluate all randomised controlled trials (RCTs) comparing the use of topical NSAIDs with placebo or any alternative analgesic interventions in adults with traumatic corneal abrasions, to reduce pain, and its effects on healing time.

Aspect Keywords Subject headings
Randomized controlled trial

Randomized OR Randomised OR
Placebo OR Randomly OR  Trial OR Groups

Randomized controlled trial
  AND  
Eye, Eye Injuries

Eye(s) OR Cornea(s) OR
injury(ies) OR abrasion(s) OR erosion(s) OR trauma(s)
OR wound(s) OR foreign

Cornea OR
Corneal Diseases OR

Wounds and Injuries OR
Eye Injuries

  AND  
Anti Inflammatory Agents

Nsaid OR
nonsteroidal anti
inflammator OR
non
steroidal antiinflammator OR
diclofenac OR

fenoprofen OR  flurbiprofen OR

indomethacin OR  ketoprofen OR

ketorolac OR  piroxicam OR

bromfenac OR nepafenac OR

oxyphenbutazone OR suprofen

anti inflammatory agents non steroidal/ OR
diclofenac OR

indometacin OR

ketoprofen

  AND  
Analegsia

Analgesia OR
Pain

Analgesia OR
Pain

Appendix 3  gives the published version of the full search as run on the OVID Medline database.


[1] Wakai A, Lawrenson JG, Lawrenson AL, et al  Topical non-steroidal anti-inflammatory drugs for analgesia in traumatic corneal abrasions. Cochrane Database Syst Rev. 2017 May 18;5:CD009781.  doi: 10.1002/14651858.CD009781.pub2.

‘ Wound Cleansing for Pressure Ulcers’ [1]

Identify and group the main keywords and subject headings

 

Aspect Keywords Subject headings
Wound cleansing

Normal saline  OR
Povidone  OR
Water  OR

Soap* 

Solutions   OR
Alcohols   OR
Water   OR

Soaps 

  AND  
Pressure Ulcers

Pressure ulcer*  OR
Pressure sore*    OR

Bed ulcer*   OR  bed sore* OR bedsore*

Decubitus ulcer* 

Pressure Ulcer 

Appendix 4  gives the published version of the full search as run on the CINAHL Ebsco database.


[1] Moore ZEH, Cowman S. Wound cleansing for pressure ulcers. Cochrane Database of Systematic Reviews 2005, Issue 4. Art. No.: CD004983. DOI: 10.1002/14651858.CD004983.pub2

Search strategies are created according to the specifications of the database, for example whether * or $ is the truncation symbol; whether subject heading searching is possible; range of filters/limits offered etc. See the on-screen help tutorials for each of the databases.  Give yourself plenty of time to become familiar with the structure of the different databases.

Testing the Search Strategy on a Group of Documents

Looking out for other search terms / subject headings

See Scoping the topic. Look at the set of results and again, look out for:

  • concepts that appear in the results which are peripheral to your topic
  • concepts within your topic which are missing from the results

Look at relevant records and identify the keywords and subject headings – make sure these are included in your search strategy.

Strategies vary between highly sensitive (high recall, but will retrieve irrelevant items) and highly specific (very precise, but may miss potentially relevant items)

The Cochrane Handbook (6.4.4) defines sensitivity versus precision as a balance between comprehensiveness and maintaining relevance[1]


[1] Lefebvre C, Manheimer E, Glanville J. Chapter 6: Searching for studies. In: Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions. Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Available from http://www.cochrane-handbook.org/   

Search Filters

Search Filters – sit on top on your subject searches

Carry out your subject searches first, evaluate and make sure you are happy with the relevancy of the results.  Then apply an appropriate filter to focus or narrow the results further. Filters are often inbuilt into databases menus and search screens. In PubMed Medline for instance you can refine searches from a menu of “article Types” or “Clinical Query” study types. In the CINAHL database on EbscoHost for example you can select from a variety of “Clinical Queries or research designs such as “Randomized Controlled Trials.”

Cochrane for instance presents some highly sensitive search strategies for identifying randomized trials in PubMed, Embase and PsycInfo.  Available at  https://work.cochrane.org/pubmed/

Expanding your Results

Using Core Articles

Once you have identified the core articles, you can expand your results further by using:

  • Reference lists: check out the reference lists in your core articles for other articles which may have been missed from your search strategy
  • Cited by: use the citation search in Web of Knowledge and SCOPUS databases and the cited by links in GoogleScholar to find out who has cited your core articles in their work
  • Related citations: a weighted algorithm is used to retrieve other items which are closely related to your item.  Treat with caution, however, as the results may be on a tangent. (Not available in all databases)
  • Contact authors and organisations: for further information on their research
  • Handsearching: manually searching relevant journals to capture articles which may have been missed in a database search.  See the Cochrane Handbook (6.2.2.1) for more details.[1]

[1] Lefebvre C, Manheimer E, Glanville J. Chapter 6: Searching for studies. In: Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions. Version 5.1.0 [updated March 2011]. The Cochrane Collaboration, 2011. Available from http://www.cochrane-handbook.org/     

Translating your Search into Other Databases

Before running searching in other databases, be confident that you have refined your ideas and terms sufficiently to retrieve good results in the primary core database.

It is a complex task to “translate” a search from one database to another and requires a lot of time and effort.  Essentially, you need to start again with each database.  Find out about the database structure and use your exploration of keywords, subject headings and filters on one database to start exploring the next. 

Each database provider (eg OVID, Ebsco) structures the databases differently. 

For example:

  • OVID databases (Medline, PsycInfo): default search is by subject heading
  • EBSCO databases (Medline, CINAHL, Ebsco): default search is by keyword
  • PubMed database (Medline): default search is a combination of subject heading and keyword
  • Elsevier Embase database: default search is a combination of subject heading and keyword

Each database (Medline, CINAHL, PsycInfo, Embase) has a different set of subject headings.

Some databases (Web of Knowledge, SCOPUS, ERIC) don’t use subject headings, so you are relying on searching authors’ words – remember to think of different words to describe the topic.