Researching for your literature review: Develop a search strategy

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 Meticillin-resistant Staphylococcus aureus (MRSA) in aged care homes.

Treat each component as a separate concept so that your topic is organised into separate blocks (concepts).

For each concept block, 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).
 

As part of the process of developing a search strategy, it is recommended that you keep a master document of search terms for each key concept. This will make it easier when it comes to translating your search strategy across multiple database platforms. 

Concept map template for documenting search terms

Boolean operators are used to combine the different concepts in your topic to form a search strategy. The main operators used to connect your terms are AND and OR. See an explanation below:

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.

See the website for a demonstration of the function of AND/OR/NOT: Combine the search terms using Boolean

By using a truncation symbol 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. Some tips about truncation:

• The truncation symbol is generally an asterisk symbol * 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. Example: 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. Example: strateg* will retrieve strategy, strategies, strategic, strategize etc.
• 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. Always use OR instead of truncation where the root word is too small e.g. ill OR illness instead of ill*

There are also wildcard symbols that function like truncation but are often used in the middle of a word to replace zero, one or more characters.

• Unlike the truncator which is usually an asterisk, wildcards vary across database platforms
• Common wildcards symbols are the question mark ? and hash #.
• Example:  wom#n finds woman or women, p?ediatric finds pediatric or paediatric.
   

For additional operators and database syntax, see the relevant section of the Systematic Review guide.

See the Database search tips for details of these operators, or check the Help link in any database.

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 selected from a controlled list 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.

Subject heading searching is important as a complimentary search method to keyword searching. This is because authors can use different words to describe the same concept. If not all relevant keywords are identified, relevant literature might be missed. Since all relevant articles will be tagged with the subject heading, a subject heading search will retrieve all articles indexed with this concept, regardless of the words contained in the titles/abstracts.

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)

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

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

A search strategy is the planned and structured organisation of terms used to search a database.

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

You will use a combination of search operators to construct a search strategy, so it’s important to keep your concepts grouped together correctly. This can be done with parentheses (round brackets), or by searching for each concept separately or on a separate line.

The above search strategy in a nested format (combined into a single line using parentheses) 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*")