Systematic literature searching

Having defined a clear, well-formulated research question, or series of questions will help you to formulate a search.

Start by doing a quick search of OneSearch to get a feel for the amount and type of literature you may find.

• Break down your research topic into separate concepts (each concept will be a separate set in your search)
• Establish your search terms for each set
• Decide on any limits to your search
• Set out your search strategy in a spreadsheet or table

You may have completed a PICO table to help define your question. This can be used in full or in part to formulate your search. You may not need to include all elements of your question in your search.

The search terms or keywords will need to take account of:

• Broader and narrower terms. For instance, "Natural disasters" is a broad term and earthquakes, floods, hurricanes are narrower terms within "Natural disasters".
• Synonyms and near synonyms. Such as workers, employees, personnel.
• UK and US English. Spellings, variations in terminology.  For example, what the British call "mobile phones" are "cell phones" in the USA.
• Changes in terminology over time. For instance, "Manic depression" is now called "Bipolar disorder".

Also consider that the field you search in a database will affect the number of results you retrieve.

For example:

• All fields: Your keywords may appear in any field. This will return a high number of results.
• Title/abstract: If keywords appear in the title and abstract, the item is likely to be highly relevant. Relies on well written, descriptive titles and abstracts.
• Keyword: Searches for your keyword in the author supplied keywords.  
• Specific fields exist in each subject database, such as Tests & Measures (PsycINFO)

Truncation (or stemming) means entering the stem of a word plus a truncation symbol so that you retrieve other forms of the word:

Example: comput* will retrieve computer, computers, computing, and computational

A Wildcard does a similar trick within a word:

Example: wom$n will retrieve both women and woman

In most databases, putting words into double quotation marks searches for that exact phrase, for instance "Assertive community treatment" or "Users' perspective".

In many databases you can also specify that you want to find words close to each other but not necessarily directly alongside.  In the examples above, searching for the exact phrase would not retrieve relevant expressions such as "assertive treatment in the community" or "from the perspective of the users and their families".

You can retrieve them by using proximity or adjacency indicators. 

These differ in each database. Check the Help in each database for exactly how to do this. 

user NEAR/3 perspective

​or

user N3 perspective 

or 

user adj3 perspective

will all retrieve records where user occurs within 3 words of perspective. 

In many subject areas, especially psychology, health and medicine, you are expected to use the thesaurus or system of subject headings in the databases. These systems of subject headings are valuable because:

• They use consistent terminology.  So articles which talk about cancer or tumours or leukaemia will be mapped to the Medical Subject Heading [MESH] term Neoplasms.

• They have a tree structure.  So you can look up Neoplasms as a MESH term and you will see that if you explode the term you will search for all the cancers in one go.

• The subject headings chosen reflect what the article focuses on.  So an article of 8,000 words might be given 20 headings in MESH.

• If you already know of some good papers in your area (“citation pearls”), look them up in a database and see what subject headings have been applied.  They may help you construct your own search strategy.

• There's more about using a thesaurus in the database guides which you’ll find in the online help available within each database

• If you are expected to retrieve all the literature on your subject, you should use a combination of thesaurus terms and free text or keywords.  This is because:

  • the most recent items may not be indexed yet

  • the concept you are studying may not be in the thesaurus

  • indexing changes over time

  • errors in indexing do happen.

The Boolean operators AND, OR and NOT are used to combine terms in a database search.

Search for individual terms or concepts first and then go to the search history and combine the sets using Boolean operators.

This video from the University of Auckland shows you how Boolean operators work.

Ways in which you might limit your search

• By date. If a thorough review article in your area was published in 1998, you could reasonably focus on material published after 1997. Or if the legislation on your area changed in 2003, then you  want material published after the new legislation came into force.
• By country or area.  If you are only interested in particular countries, you can often limit your search by geographical area.
• By age group.  Many databases allow you to state that you only want material about (say) children or elderly people.
• Human/animal studies.  Particularly useful in medical/life sciences work.
• By language. Do you just want material in English?  However if you are doing a thorough or systematic review, you may find that there are useful articles written in foreign languages.  They will often have an abstract in English which gives useful insights, or you may need to get a key paper translated. Consider the bias you will introduce to your search is you only include results published in English. 
• By type of document. For instance, do you just need peer-reviewed articles?
• By field. Databases allocate the different elements of a record to a specific field.  You can then specify which field is to be searched for a particular term. This screens out irrelevant material - for instance if you want material by an author called London put London into the author field, so you avoid all the articles about the city.
• By methodology Do you just need quantitative studies? Or qualitative studies?  It is NOT enough to simply add "qualitative" or "quantitative" to your search terms.  The article may not mention the actual word. So to restrict your search to qualitative studies add in words for methods used in a qualitative study such as questionnaire* OR survey* OR interview* OR "focus group*" OR "case stud*" OR observ* OR "grounded theory" OR narrative OR thematic OR experienc* OR "content analysis" OR ethnolog* as well as Qualitative.

Methodological search filters (hedges)

These are search strategies for identifying studies using specific methodologies, such as randomised controlled trials. These are usually developed, tested and published by information specialists, and will often relate to one specific database.

The InterTASC Information Specialists' Sub-Group (ISSG) maintain this useful Filters resource containing details of methodological search filters and associated discussion.

Published systematic reviews will often contain a description of the terms used, or an example search strategy from one of the databases. You can use a published search to help formulate your own strategy. Bear in mind that you may have different conceptual approaches which would affect the search. Also, authors may offer a critique of their own search strategy which should be taken into account.

Full search strategies for one or more databases searched will usually be included as a supplementary file or appendix to the journal article. Search strategies will usually show the database-specific syntax and field codes as well as the terms used and the operators used to combine them.

Example: