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Systematic reviews - searching for literature: How to search databases (Part 2)

So what do I do with my search terms?

The diagram below shows a very simple search. Each primary topic from the research question is give a column which we call a facet. Within each facet, the like terms are joined together using OR. This gives us a total for each facet individually. We then overlap the totals of each facet using AND. In this example we are only using two facets, the population/problem and the intervention. You don't necessarily know all your subject headings at this stage and may not include them here (but for this example we know what we are going to include).

Question: Do cranberries reduce the prevalence of urinary tract infections in women?

Limits: Women

Have a look at the next tab 'Example search in Medline' to see how the search words would be using in a database. The example includes both keyword searching and subject heading searching.

Combining your search terms

Boolean OR
OR combines like concepts together. Each smaller circle represents the results that are returned for any given term searched for a particular facet in your search. Linking them with OR joins them all together in one set represented by the big circle.


Combining your search terms

Boolean AND
AND links different concepts together (which you have linked with OR). The area in the centre where the circles cross represents the results that contain a concept from both facets.


Developing and refining your search

Boolean NOT

In general, it is best not to use the boolean NOT operator. If you are considering doing so, please contact one of the librarians who supports your Faculty. The primary problem with this operator is that it cannot identify if two terms are being used in a single article so for example, if you were looking for articles about women not men, and used the NOT men option, if an article was talking about both women and men, it would be removed (because it mentioned men) which is not what you want.

Databases offer may ways to refine a search. In general, we use very few of these. The principle limiters you might use are:

  • Year of publication
  • Peer review (if a database indexes non peer review material)
  • Language (possibly, but really if a paper looks essential it should be translated if it is not a language you can read).

Do remember though, all limiters run the risk of excluding relevant material. It is best to start with no limiters and only apply them if you really need to .

DO NOT limit to full text if the option is available. Use an inter library loan service.

Limiting by research method:

There is not really a consistent way to do this across databases. Some like Medline do include methodology filters that have been developed with varying degrees of sensitivity/specificity/optimisation. Research into the development of filters of this type is ongoing and a useful site to look at is ISSG Search Filters Resource . Do note however that applying a limiter like this should be used with caution and it would be worth consulting with a librarian who supports your faculty.

Further links: