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Systematic Reviews

A guide to conducting systematic reviews at the University of the Sunshine Coast

1. Developing Answerable Questions

A technique often used in health research for formulating a clinical question is the PICO Model.

Using PICO, a clinical question will have 4 elements:

  • Patient/Population - Who or what population
  • Intervention - What are we doing to them
  • Comparison – Alternative intervention (or none)
  • Outcome – Methods of measuring the results

Example question: For adult Type 1 diabetics (P), are insulin pumps(I) or traditional insulin therapy (C) more effective in control of blood glucose(O) ?

PICO is a method of putting together a search strategy that allows you to take a more evidence based approach to your literature searching when you are searching databases like CINAHL and PubMed

More information...

Centre for Evidence-Based Medicine - Formulating Answerable Clinical Questions
HealthLinks, University of Washington - Construct Well-Built Clinical Questions Using PICO

 

For other non-clinical or questions of a qualitative nature, an alternative, PCC may work better:

  • Patient/Population - Who or what is the population or thing you are interested in
  • Concept - What about this population are you interested in?
  • Context - What are the time geographical or other boundaries or limits?

Example question: Do Australian emergency nurses believe they benefit from an induction mentoring program.

P=nurses, or it could be seen as "emergency nurses"; Concept= beliefs about benefits of an induction mentoring program; Context = Australia, or Australian emergency hospital settings...

Note: This is much harder to analyse to get useable search terms than the PICO example above.  It is common that a qualitative style of question like this will be harder to analyse, and therefore it's harder to develop good search terms.

2. Identify Synonyms and Related Terms

It is important not to overlook this stage in the search process. Time spent identifying all possible synonyms and related terms for each of your PICO elements or concepts will ensure that your search retrieves as many relevant records as possible.

 - Think laterally about how others may describe the same concept
 - What terminology is used internationally?
 - Are there spelling differences in UK English and US English words?
 - Are there any colloquial terms or phrases used?
 - Check the search terms used in other papers or systematic reviews - other terms may be suggested from these.

It might be useful to check relevant dictionaries, encyclopedias and key texts for alternate terms.

Build a list of each of the search terms you identify. For example, if you were searching for:

 Exercise-based rehabilitation 
for  coronary heart disease 

Your list of synonyms and related terms might include:

 Exercise-based rehabilitation Coronary heart disease

      rehabilitation

      exercise

      exercise therapy

      sports

      physical education and training

      exertion

      physical training

      aerobics

      kinesiotherapy

           

      coronary heart bypass

      myocardial ischemia

      myocardial infarction

      coronary disease

      coronary thrombosis

3. Use Truncation and Wildcards

The definition of ‘truncation’ is to shorten or cut-off at the end. Truncation is used in database searches to ensure the retrieval of all possible variations of a search term.  All databases allow truncation, but the symbols used may vary, so it is best to check the database help for details.

Databases usually allow words to be truncated either at the end, or internally:

  • Truncating a word at the end ensures that all variations of the word, beginning with a specific root, will be retrieved. This is particularly useful for retrieving singular and plural versions of words.

Be careful not to truncate terms too early, or you may retrieve a high number of irrelevant documents.

Most databases use an asterisk (*) to find alternate endings for terms. For example:

therap* will retrieve therapy, therapies, therapists, therapeutic, therapeutical, etc



  • Truncating a word internally ensures that any variations of spelling of a word can be retrieved. For example, pediatrics or paedetrics

Internal truncation is available in some databases, allowing you to search for alternate spellings of words - extremely useful when searching for American and English spellings of words.

For example, using the OVID databases (MEDLINE, EMBASE, PsycINFO, etc), a question mark included within a word can designate zero or one character in that place:

colo?r will retrieve either colour or color

4. Combining Terms

Boolean Operators

Boolean operators allow you to link terms together, either to widen a search or to exclude terms from your search results.

 

OR   

 
OR - Boolean Operator

 

Use to broaden your search, increasing the number of references retrieved. Use "OR" to search for synonyms and related terms for each concept within a research question.

For example, when searching for the concept "exercise based rehabilitation" you might use the following terms:

rehabilitation OR exercise OR exercise therapy OR sports OR exertion OR physical training OR aerobics OR kinesiotherapy

AND   And - Boolean Operator

Used to narrow a search, therefore decreasing the number of references.

For example, searching for:
coronary heart disease AND Australian Aboriginals

Would retrieve just those references covering both topics.

 NOT     Not - Boolean Operator

Used to narrow a search, therefore decreasing the number of references.
For example:

female NOT male

Would retrieve references dealing with females, but not those which discuss males. Caution should be exercised when using NOT, In the example above, research dealing with both females and males would be excluded from the search results.

 

Nesting

Nest search terms to control the logic of your search. For example: Remembering to put phrases in quotes and using * for plurals and other variants...

(rehabilitation OR exercise OR "exercise therapy" OR sport* OR "physical training")

AND

("Coronary heart bypass" OR "myocardial ischemia" OR "myocardial infarct*" OR "coronary disease" OR "coronary thrombosis")

5. Identify Search Limits/Exclusion Criteria

You should next think about the limits you intend to apply to your search.

You should have a reason or justification for any decision to exclude references.

Common exclusion/inclusion criteria include

  • Language: Articles in English only; or include others
  • Date range: "Last 10 years" might be justifiable in a fast changing field with a lot of publications, but this is not always the case.
  • Type of publication: The type of review and availability of evidence will play a big role in this decision.
  • Geography: If your stated focus is Australia you can exclude others. 

All exclusions must be clearly stated and justified in the text

 

6. Keyword vs Subject Searching

Controlled vocabularies (such as the MESH subject headings used in Medline/Pubmed, CINAHL term list, and the PsycInfo Thesaurus) provide an organised approach to the way knowledge is described. 

Their use is extremely important as they bring uniformity to the indexing of publications included within a database. Using the same terminology throughout a database creates consistency and precision and helps you to find relevant information no matter what terminology the author may have used within their publication.

Indexing is usually a manual process. Databases such as MEDLINE employ specially trained indexers to read the full-text of each publication then identify all of the concepts covered within the article. These concepts are then translated to the controlled vocabulary used within the database. It is the indexer’s job to ensure that each concept included in the article are identified and assigned a term.

Each database may use different subject headings to describe the same concept. As an example, the term “complementary medicine”:

The MESH heading (MEDLINE) is “complementary therapies”
The CINAHL heading is “alternative therapies”


Pubmed, CINAHL and some other databases provide a search option to “explode” terms.  Exploded searches retrieve indexed records for a term, plus other terms which are a derivative (more specific, narrower terms) of the search term. Exploding search terms provides a fast way to find related concepts in a single search.

For example, if a search for "complementary therapies" in MEDLINE was exploded:

The search results would also include records  indexed with the MESH headings acupuncture”, “anthroposophy”, “auriculotherapy”, and so on.

 

NOTE: Clicking on a MESH heading will display its tree, including the exploded terms.

 

 

Keyword searches are extremely important when conducting systematic reviews, and should be used in combination with the relevant subject headings within each of your database searches:

  • Authors may not describe their methods or objectives well and indexers are not always experts in the subject areas
  • The available indexing terms might not correspond to the terms the searcher wishes to use. Cochrane Handbook for Systematic Reviews of Interventions (2008, p. 130)

Search Filters

The following sites include examples of pre-tested search filters.

Reporting Bias

Types of reporting bias include:

  • Publication bias
  • Time lag bias
  • Multiple (duplicate) publication bias
  • Location bias
  • Citation bias
  • Language bias
  • Outcome reporting bias.

For details see: Cochrane Handbook for Systematic Reviews of Interventions (2008, Chapter 10)

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