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Researching for your literature review: Search strategy

Developing a search strategy - Health/Medical topic example

Identify key terms and concepts

Start developing a search strategy by identifying the key words and concepts within your research question. The aim is to identify the words likely to have been used in the published literature on this topic.

For example: What are the key infection control strategies for preventing the transmission of Methicillin-resistant Staphylococcus aureus (MRSA) in aged care homes.

Treat each component as a separate concept (there are usually between 2-4 concepts).

For each concept list the key words derived from your research question, as well as any other relevant terms or synonyms that you have found in your preliminary searches. Also consider singular and plural forms of words, variant spellings, acronyms and relevant index terms (subject headings).
 

Search concept 1 Search concept 2 Search concept 3
KEYWORDS KEYWORDS KEYWORDS
infection control methicillin resistant staphylococcus aureus aged care homes
infection prevention meticillin resistant staphylococcus aureus nursing homes
MRSA
MESH TERMS MESH TERMS MESH TERMS
exp Infection Control/ Methicillin-resistant Staphylococcus aureus/ homes for the aged/
    nursing homes/

Combine search terms with OR / AND / NOT (Boolean operators)

boolean operators infographic

OR  

  • Link keywords related to a single concept with OR
  • Linking with OR broadens a search (increases the number of results) by searching for any of the alternative keywords

Example: nursing home OR aged care home

AND

  • Link different concepts with AND
  • Linking with AND narrows a search (reduces the number of results) by retrieving only those records that include all of your specified keywords

Example: nursing home AND infection control

NOT  

  • using NOT narrows a search by excluding results that contain certain search terms
  • Most searches do not require the use of the NOT operator

Example: aged care homes NOT residential homes will retrieve all the results that include the words aged care homes but don't include the words residential homes. So if an article discussed both concepts this article would not be retrieved as it would be excluded on the basis of the words residential homes.

 

truncation and wildcard infographic

Use symbols to retrieve word variations

Truncation - By using truncation you can capture all of the various endings possible for a particular word. This may increase the number of results and reduce the likelihood of missing something relevant.

The truncation symbol is commonly an asterisk * and is added at the end of a word.

It may be added to the root of a word that is a word in itself e.g. prevent* will retrieve prevent, preventing, prevention preventative etc.

It may also be added to the root of a word that is not a word in itself e.g. strateg* will retrieve strategy, strategies, strategic, strategize etc

Note: If you don't want to retrieve all possible variations, an easy alternative is to utilise the OR operator instead e.g. strategy OR strategies.

 

Wildcard  - Wildcard symbols include the question mark ? and hash #. They replace zero, one or more characters in the middle of a word.

Example:  wom#n finds woman or women, p?ediatric finds pediatric or paediatric.

The symbols may vary in different databases - See the Database search tips for details, or check the Help link in any database.

Use quotes to keep word order when searching for phrases

For words that you want to keep as a phrase, place two or more words in "inverted commas" or "quote marks". This will ensure word order is maintained and that you only retrieve results that have those words appearing together.

Example: “nursing homes”

There are a few databases that don't require the use of quote marks such as Ovid Medline and other databases in the Ovid suite. The Database search tips provides details on phrase searching in key databases, or you can check the Help link in any database.

Identify appropriate Subject Headings (index terms)

Many databases use subject headings to index content. These are generally selected from a controlled list by experienced indexers and describe what the article is about. 

A comprehensive search strategy is often best achieved by using a combination of keywords and subject headings where possible.

In-depth knowledge of subject headings is not required for users to benefit from improved search performance using them in their searches.

Advantages of subject searching:

  • Helps locate articles that use synonyms, variant spellings, plurals
  • Search terms don’t have to appear in the title or abstract

Note: Subject headings are often unique to a particular database, so you will need to look for appropriate subject headings in each database you intend to use.

Subject headings are not available for every topic, and it is best to only select them if they relate closely to your area of interest.

MeSH (Medical Subject Headings)

The MeSH thesaurus provides standard terminology, imposing uniformity and consistency on the indexing of biomedical literature. In Pubmed/Medline each record is tagged with MeSH (Medical Subject Headings).

The MeSH vocabulary includes:

  • Headings (also called main headings or descriptors)
    • Represent concepts found in the biomedical literature
    • Some headings are commonly considered for every article (eg. Species (including humans), Sex, Age groups (for humans), Historical time periods)
  • Subheadings (also called qualifiers)
    • attached to MeSH headings to describe a specific aspect of a concept
  • Publication characteristics/types
    • describe the type of publication being indexed; i.e., what the item is, not what the article is about (eg. Letter, Review, Randomized Controlled Trial)
  • Supplementary concept records
    • Terms in a separate thesaurus, primarily substance terms

 

Identify useful limits

Many databases provide system based limits. Adding a limit to a search will exclude certain material not relevant to your research question, and therefore reduce the number of results. These functions vary from database to database but often appear on your initial search screen or beside your search results.

Examples include:

  • limiting to English language
  • limiting by publication date
  • limiting to a specific document type
  • limiting your search to specific fields, such as only searching in the Title/Abstract fields

The use of limits should be justified by the focus of your research and any constraints.

It is useful to build a ‘sample set’ or ‘gold set’ of relevant references before you develop your search strategy.

Sources for a 'sample set' may include:

  • key papers recommended by subject experts or supervisors
  • citation searching - looking at a reference list to see who has been cited, or using a citation database (eg. Scopus, Web of Science) to see who has cited a known relevant article
  • results of preliminary scoping searches.

The papers in your 'sample set' can then be used to help you identify relevant search terms

  • Look up your 'sample set' articles in a database that you will use for your literature review. For the articles indexed in the database, look at the records to see what keywords and/or subject headings are listed.

The 'sample set' will also provide a means of testing your search strategy

  • When an article in the sample set that is also indexed in the database is not retrieved, your search strategy can be revised in order to include it (see what concepts or keywords can be incorporated into your search strategy so that the article is retrieved).
  • If your search strategy is retrieving a lot of irrelevant results, look at the irrelevant records to determine why they are being retrieved. What keywords or subject headings are causing them to appear? Can you change these without losing any relevant articles from your results?

An example of a search strategy incorporating all three concepts, that could be applied to different databases is shown below:

screenshot of search strategy entered into a database Advanced search screen

The above search strategy in a nested format (for use in a single search box) would look like:

("infection control*" OR "infection prevention") AND ("methicillin resistant staphylococcus aureus" OR "meticillin resistant staphylococcus aureus" OR MRSA) AND ( "aged care home*" OR "nursing home*")

The following video will present a range of resources and advanced search strategies to help you find information for your literature reviews. Approximate running time 20 minutes.