4. How do I search for the evidence?
4.6. Limits and filters
5.6 Limits and filters
You can apply limits and filters to ensure that you have fewer irrelevant results to look through. Most databases offer the ability to refine your search results using different parameters:
The most commonly used limit is publication date – you can limit your search results to articles published in a particular year range. However, it is important to remember that older papers may still be valid and relevant.
Some databases allow you to limit by geographical area (for databases which use subject headings, there are usually geographical subject headings which you may wish to use). However, bear in mind that you may exclude some relevant articles when you limit by geographical area.
Most databases allow you to limit your results to publications in specified languages. In systematic reviews it would not be acceptable to apply language limits, as here you would need to report all the publications retrieved regardless of the language, so that others who might speak the languages could potentially appraise the evidence available.
In some databases you can also restrict to certain publication types or study types such as journal article, conference paper, randomised controlled trial, meta-analysis or review, though this is not always reliable.
Some databases allow you to apply search filters (also called methodology filters) to your search. Search filters are pre-created search strategies which can be used to retrieve particular types of study, such as systematic reviews or meta-analyses. You can use the help pages of the different databases to find out which filters are available in that database. For example, the publishers of CAB Abstracts have produced a search filter to retrieve systematic reviews or meta-analyses in CAB Abstracts and Global Health called CABI filters (pdf).