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Nursing and Allied Health: Supplementary on Systematic Literature Searching

Guide to NUS Libraries' Resources for Nursing

Filters and Hedges

Filters and hedges are search strategies that have been devised and tested to filter the results of your search from large, general purpose databases. They can help you quickly search databases for articles on certain topics or those with certain study designs.

According to Cochrane Handbook 4.4.7, "search filters should be used with caution. They should be assessed not only for the reliability of their development and reported performance, but also for their current accuracy, relevance and effectiveness given the frequent interface and indexing changes affecting databases."

Systematic Searches #9: Using Filters and Hedges (Video)

This tutorial from the The Medical Library at Yale University introduces the concept of filters and hedges, their validation process, and where to find existing filters and hedges.

They are very useful when they are used appropriately, you should always evaluate a hedge before using it by asking the following questions:

​1. What is the validation process?

2. What is the sensitivity and specificity scores?

3. Which database is the hedge developed and validated in?

4. Can you use it for the subject area you are going to search in?

5. When was the hedge developed--would it still be valid?

Existing filters and hedges

The following list of resources are being mentioned in the above video by the The Medical Library at Yale University.

For more resources, please refer to the NUS Systematic Reviews Libguide on "Useful search filters by study design and topic".

The best-known methodological hedges are the "clinical queries" developed and validated by Haynes and colleagues at McMaster University.

This blog has been created to share PubMed search strategies. 

The Search Filter Resource aims to provide easy access to published and unpublished search filters. It also provides information and guidance on how to critically appraise search filters, study design filters in progress and information on the development and use of search filters. Inclusion of a search filter is not an endorsement of its validity or a recommendation.

The search filters used by SIGN are developed in-house or are created by other research organisations and adapted to meet SIGN information needs. SIGN's filters may provide less sensitive searches than used by other systematic reviewers such as The Cochrane Collaboration, but enable the retrieval of medical studies that are most likely to match SIGN's methodological criteria.

Qualitative filter compiled by NUS Medical Library

There are two Methods to search for qualitative studies:
A. Use Built-In Filters ( available in the databases)
B. Apply filters which are adapted from published sources and to combine with Boolean Operator "AND" to complete your search.

Cochrane work on RCT filter

In CENTRAL you need not use an RCT filter because all the records are thoroughly and correctly indexed. This means you can just limit your search to study type.