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Systematic Literature Searches

Search construction

There are some basic syntax that will work over most databases. Using them will help you finesse your search. These are:

  • Truncation & wildcards

  • Phrase searching

  • Proximity operators

Truncation- using wildcard symbols to replace one or more letters

Example: 

behavio* will find behavior, behavioral, behaviour, behavioural, etc.

Some databases will allow wildcards within words or at the start of words. 

Example:

Organi*ation will find organization or organisation 

Phrase search is used when you want to ensure the database searches for precisely the text you have written.

Phrase search is particularly good for composite terms

Example:

“gothic fiction” vs gothic OR fiction

NEAR, the proximity operator. This specifies that two words must be within a certain distance of each other. 

It’s useful for when you need to contextualise your search, or if you’re looking for two keywords/topics that may sometimes appear in the same page but not in relation to each other.

Example:

Operating NEAR/2 system

Combining your keywords - Boolean operators

Databases use Boolean operators to combine your search terms. They are used to broaden or narrow your searches.

The Boolean operators are: AND, OR, NOT.  

AND narrows your search result. AND denotes the intersection - both your keywords must be present. Your search will become more precise than if you were to search for each keyword individually:

OR broadens your search. Or denotes the union - here just one (or both) of your keywords needs to be present. Your search result will become larger and broader:

NOT limits your search. NOT denotes the set difference. Here the keyword that follows this Boolean operator must not be present in the results. NOT filters out unwanted search results (noise), but you must use it with care, it is easy to filter out relevant results:

         

You can use multiple operators in the same search, but if you are using both AND and OR in the same search string, then it is important to place brackets around the words that belong together in an OR block.

Example:

  • (astma OR allergy) AND children

Text word searching

All databases allow you to search using text words or keywords. You can often search for words in various fields such as titles, abstracts, notes and keywords, etc.

Each database is different so take the time to see which field are searchable. Searching the “full text” directs the database to look at all fields in an article so your results would be very broad. Conversely if you search the title or abstract fields your results would be more focused.

Field searches can also be used to scan through some very specific fields such as ”Geographic Terms”, ”CompanyEntity” or ”Conference location”, thus minimising non-relevant results in your search.

Below is an example of the fields you can search in the database Proquest

Subject Headings

Some databases allow you to search using subject headings. These are common in health-related databases such as PubMed, Medline and CINAHL.

Subject headings or controlled subject terms are the "pre-selected" keywords the database owners have attached to the individual references to denote what a document "is about". 

The subject headings are selected from a controlled vocabulary. They ensure that you can create consistent subject searches, as references on the same subject can then be found with the precise same keyword, irrespective of the wording in titles and abstracts.

Subject headings vary from database to database, and you cannot expect a search term used as a subject heading in one database to be found as a subject heading in another database.

The list of controlled subject terms may be hierarchically organised into a thesaurus. Here you can choose between more generalized broader terms (BT) or more specific narrower terms (NT). Thesauri are mainly found in the fields of medicine, psychology and the natural sciences,  and education.

Should I choose full-text search or use controlled subject terms?

If you need to find "everything" on a particular subject, for a systematic review for instance, then you will need to use both controlled subject terms and full-text search. But in other cases there may be a good argument for choosing one or the other approach, depending on what you are working with. Generally speaking, you can say:

  • A search on subject headings will give fewer, but much more precise results.
  • Text word searching will give many more search results, but also a lot of "noise" (i.e. non-relevant references). This can be controlled by limiting the field you search e.g.  title only
  • If you work within a field where the terminology is consistent, it may be a good idea to use the controlled subject term.
  • If you are working in a field with changeable or ambiguous terminology, or if your work is multidisciplinary in nature, it may be an advantage to carry out text word searches.

Below is brief and succinct video explaining the difference between database subject headings and textwords

Translating your search.

Depending on your subject you many need to search various databases. Each database will differ in their search interface and structure. Search syntax can also differ between different databases.

Below is a guide to the differences in search command and syntax in some of the larger databases

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