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Systematic Reviews

Comprehensive search

The focused question

The example below will guide you through the process of building comprehensive search strategy in PubMed database.  PICO framework is used to formulate the focused question to help you build an effective search strategy to find relevant studies that meet the eligibility criteria for your review topic. 

 Does the use of light therapy help to improve sleep disturbances for dementia patients? 

P(Population/ Patient)

I(Intervention)

C(Comparator)

O(Outcome)

Dementia / Alzheimer's disease

light therapy

  

Usual care / placebo light

  • improving sleep disturbances
  • improving activities of daily living, cognition
  • improving depression and agitation
  • behavioral and psychiatric conditions 
  • caregiver burden

 

 

NUS Libraries - Search template

According to the PRISMA 2020 Statement (published in 2021), details of search strategy should be clearly documented.   We have designed the Search Template for you to plan your search, document the sources that you have searched, the search date and the search terms used (include both the controlled vocabulary and the keywords).

Please click on the link to download the template to follow the steps on developing the search strategy below:

Developing the search strategy

Once you have identified the most important PICO elements of your research question (i.e. the intervention and patient terms), the next step is to brainstorm for keywords to come up with an extensive list of vocabulary to fill in the search template shown below.  The more relevant and appropriate keywords are, the more comprehensive the search strategy will be.  

For systematic review, the same keywords can be used to replicate the search across all databases. 

 

 Concept 1

 /Population/Problem

 Concept2

/Intervention/Exposure

Key concepts

Identify the key concepts based on your research topic.

Patients with dementia

 Light therapy

Free text terms / natural language terms

(synonyms, UK/US terminology, medical/laymen’s terms, acronyms/abbreviations, drug brands, more narrow search terms)

List down your keywords for each concept.

Dementia

Dementias

Alzheimer

Alzheimer’s

Alzheimers

Lewy Body

Lewy bodies

Light therapy

Light therapies

Phototherapy

Phototherapies

Bright light therapy (BLT)

 

After generating the keywords, the next step is to identify the subject headings or the controlled vocabulary or indexing terms. 

What is Subject headings

Subject headings are the list of standardized vocabulary used by the indexer to describe the content of the articles in the databases. It is used interchangeably with controlled vocabulary or indexing term.  Every database has their unique naming, e.g. iPubMed, it is known as MeSH (Medical Subject Heading). 

Subject Hierarchy

You can make use of the MeSH Database in PubMed to search for the appropriate MESH term.  This is the most precise way to find all the MEDLINE records via PubMed on a particular concept. Once the correct MeSH term is identified, click on the subject link to look out for the subject hierarchy shown below:

Dementia

AIDS Dementia Complex

Alzheimer Disease

Aphasia, Primary Progressive

Primary Progressive Nonfluent Aphasia

Creutzfeldt-Jakob Syndrome

Dementia, Vascular

CADASIL

Dementia, Multi-Infarct

Diffuse Neurofibrillary Tangles with Calcification

Frontotemporal Lobar Degeneration

Frontotemporal Dementia +

Primary Progressive Nonfluent Aphasia

Huntington Disease

Kluver-Bucy Syndrome

Lewy Body Disease

The subject terms are arranged in hierarchical order to show the broader and narrower terms.   This is known as subject hierarchy. E.g. ‘Dementia’ is a broader term with the narrower terms indented underneath.  When you search ‘Dementia’ as a MeSh term, all studies on dementia, include both general and specific will be found.  Unlike subject heading, search using keyword will only return you articles in which the word is used.  You will miss studies which may use different terminologies to describe the same concept.  Nevertheless, keyword complements the use of subject headings as it retrieves the latest studies which will usually be missed as it takes time for indexer to index the articles. 

For systematic review, both the MeSH and keywords should be combined to build a comprehensive search.

Based on the list of MeSH terms and the keywords identified, the next step is to build the search strategy as follows:

1.Search strategy for ‘P’ term (i.e. dementia) 

P (Population)

Building Search Statement for ‘P’

MeSH

"Dementia"[Mesh]

Keywords

Dementia OR Dementias OR Alzheimer OR Alzheimer’s OR Alzheimers OR Lewy Body OR Lewy bodies

Search Keywords in [Title/Abstract]

Dementia[Title/Abstract] OR Dementias[Title/Abstract] OR Alzheimer[Title/Abstract] OR Alzheimer’s[Title/Abstract] OR Alzheimers[Title/Abstract] OR Lewy Body[Title/Abstract] OR Lewy bodies[Title/Abstract]

 

Combine MeSH and keywords within the same concept with Boolean Operator ‘OR’

"Dementia"[Mesh] OR Dementia[Title/Abstract] OR Dementias[Title/Abstract] OR Alzheimer[Title/Abstract] OR Alzheimer’s[Title/Abstract] OR Alzheimers[Title/Abstract] OR Lewy Body[Title/Abstract] OR Lewy bodies[Title/Abstract]

2.Search strategy for ‘I’ term  (i.e. light therapy)

I (Intervention)

Building Search Statement for ‘I’

MeSH

"Phototherapy"[Mesh]

Keywords

Light therapy OR Light therapies OR Phototherapy OR Phototherapies OR BLT

Search Keywords in [Title/Abstract] field

Light therapy[Title/Abstract] OR Light therapies[Title/Abstract] OR Phototherapy[Title/Abstract] OR Phototherapies[Title/Abstract] OR BLT[Title/Abstract]

Combine MeSH and keywords within the same concept with Boolean Operator ‘OR’

"Phototherapy"[Mesh] OR Light therapy[Title/Abstract] OR Light therapies[Title/Abstract] OR Phototherapy[Title/Abstract] OR Phototherapies[Title/Abstract] OR BLT[Title/Abstract]

3.Combining searches for ‘P’ AND ‘I’ with Boolean Operator ‘AND’

("Dementia"[Mesh] OR Dementia[Title/Abstract] OR Dementias[Title/Abstract] OR Alzheimer[Title/Abstract] OR Alzheimer’s[Title/Abstract] OR Alzheimers[Title/Abstract] OR Lewy Body[Title/Abstract] OR Lewy bodies[Title/Abstract]) AND ("Phototherapy"[Mesh] OR Light therapy[Title/Abstract] OR Light therapies[Title/Abstract] OR Phototherapy[Title/Abstract] OR Phototherapies[Title/Abstract] OR BLT[Title/Abstract])

Results retrieved = 308 (search last updated on 10 Oct 2021)

 

4.Refining the final search

If there is a large result set retrieved, the search strategy can be further refined depending on the type of questions being asked.  Filters are available in PubMed and most of the databases to help narrow down the search results.  Please refer to the Search Filters in the next section for more details.   

Additionally, you should also refer to the PRESS Evidence-Based Checklist for practical tips to improve the quality of your search strategy.  

McGowan, J., Sampson, M., Salzwedel, D. M., Cogo, E., Foerster, V., & Lefebvre, C. (2016). PRESS Peer Review of Electronic Search Strategies: 2015 Guideline Statement. J Clin Epidemiol, 75, 40-46. https://doi.org/10.1016/j.jclinepi.2016.01.021 

In addition to the Boolean operators, most of the subscribed databases allow searching using proximity operators which is lacking in the free databases, e.g. PubMed.  

Proximity operators is a technique use to locate the occurrence of search words that are closed by one another.  It is usually denoted by NEAR/n (n is the number of words) to find the search terms within a specific number of words of each other.  The proximity symbol may vary depends on the databases used.  Please refer to the help guide of the respective databases to look out for the correct syntax. 

Proximity operators provide an alternative to ‘AND’ operator. For example, searching (dementia NEAR/6 “sleep disorder”) will retrieve more relevant set of results than searching (dementia AND “sleep disorder”).  The former shows that ‘dementia’ and “sleep disorder” appear 6 or less words within one another.  It is more precise than the latter which is not able to show how far apart are the words from one another.

Please find below a concised summary of the proximity operators of the commonly used databases.  For more details, please refer to the NUS Libraries Database Syntax Guide below.

Databases

Discipline

Controlled vocabulary

Proximity Operators

MEDLINE(PubMed)

Biomedical and Life Sciences

MeSH

NIL

Embase

Biomedical and Life Sciences

Emtree

NEAR/n (in any order) up to (n-1) words in between​

NEXT/n (in same order) up to (n-1) words in between​

The Cochrane Library

Medical & Health Sciences

MeSH

NEAR/n (in any order) up to (n-1) words in between​NEXT/n (in same order) up to (n-1) words in between​

CINAHL(Ebscohost)

Nursing and allied health 

CINAHL Subject Headings

Nx: (in any order) up to (x) words in between​

Wx: (in same order) up to (x) words in between

PsycINFO(Ovid)

psychology and the behavioral and social sciences

Thesaurus of Psychological Index Terms

ADJ finds two terms next to each other in the specified order​

ADJn (in any order) up to (n-1) words in between​

ERIC(ProQuest)

Education

ERIC Thesaurus

NEAR/n or N/n (in any order) up to (n) words in between​

PRE/n: (in same order) up to (n) words in between​

Scopus

Multidisciplinary

NIL

W/n (in any order) up to  (n) words in between​

PRE/n (in same order) up to (n) words in between​

Web of Science

Multidisciplinary

NIL

NEAR/x (in any order) up to (x) words in between​