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Systematic Reviews: How to search?

Literature searching

Documenting and reporting the search strategy

Step One - Documenting searches

When you are conducting your searches, keep track of what you are doing by documenting your search process in enough detail to ensure that it can be reported correctly in the review.

Documentation of your search strategy should include:

  • databases used
  • date of search
  • dates of coverage provided by each database
  • search terms used
  • total publications found
  • number of relevant publications
  • limits applied

Step Two - Reporting searches

There are a number of places where searches can be reported. These include the appendix, the review abstract, the methods section or the results section. Below are some examples that show these different models:

  • this Cochrane review has both a line by line description in the appendix of the pdf (see page 195) as well as a description of databases searched in the search methods section (see page 8)
  • a textual commentary in the Results section of this article on page 217

It is advisable to use the PRISMA 2009 flow diagram for further documentation of the number of records identified by database searching and through other sources. The flow diagram depicts the flow of information through the different phases of a systematic review. It maps out the number of records identified, included and excluded, and the reasons for exclusions. Instead of filling in a manual form you can now use the PRISMA Diagram Generator to report on the results of a search for a systematic review.

A useful reporting tool for qualitative studies is STARLITE

Managing search results

 

While you are conducting your search, you will find it much easier to manage your search results using bibliographic software such as EndNote. With EndNote, you can:

  • build a library of your references which can be obtained through database searches and manual inputs
  • insert into your working paper in-text citations and bibliographic entries from the EndNote library
  • choose from over 200 referencing styles with the ability to modify styles for a style that is not included
  • identify the source of the references
  • use additional fields to customise how you would like your library to be displayed
  • create groups to organise your references under different headings

The Library offers hands-on EndNote sessions for both beginners and experienced users. See the Curtin Library workshops calendar to book a place.

Planning the search

Aim of the search

The overarching objective of a systematic review search for evidence is to identify all the studies (and all the relevant data from the studies) that pertain to the research question.

Search plan

Your search plan will be a brief summary of the topic of the study, a summary of inclusion and exclusion criteria, a list of the appropriate publications, sources and methods that you will use for identifying materials and a list of concepts related to your topic. Your search strategy will put into operation the decisions you have made in your search plan.

PICO

Begin devising your search strategy by using the PICO for quantitative research and PICo for qualitative research and ensure that the research question has been translated into search concepts.


NOTE: It may be useful to work with a librarian who has experience in a wide range of bibliographic databases and electronic information sources to plan your search strategy.

Structuring the search

Search Strategy

The aim of the search strategy is to maximise the retrieval of relevant documents and minimise the retrieval of non-relevant material. It is necessary to strike a balance between achieving comprehensiveness and maintaining relevance when developing a search strategy. Increasing the comprehensiveness (or sensitivity) of a search will reduce its precision and will retrieve more non-relevant articles.

Sensitivity is the ability to identify all the relevant studies. Specificity is the ability to exlude irrelevant studies. There is an inverse relationship between sensitivity and specificity i.e. high sensitivity will tend to have low specificity, and this means that a large number of articles retrieved are not relevant to the review question.

Inappropriate or indadequate search strategies may fail to identify records that are included in bibliographic databases.
 

1. PICO

  • It is not necessary to include all of the PICO concepts in the search strategy. It is preferable to search for those concepts that can be clearly defined and translated into search terms. Although a research question may address particular populations, settings or outcomes, these concepts may not be well described in the title or abstract of an article and are often not well indexed with controlled vocabulary terms.
     

2. Search tips

Use "Boolean" logic to express relationships between search terms.

+More information on Boolean logic

3. Restrictions
Restrictions are not advisable for:

  • language
  • date - use only if it is known that relevant studies could only have been reported during a specific time period
  • format -  include all formats. For example, excluding letters will result in missing out on important additional information relating to an earlier trial report or new information about a trial not reported elsewhere

4. Revising your search strategy

  • Your search strategy will have to be revised if:
  • Upon your judgement the retrieved items are not relevant to your topic
  • Some aspects seem to be missing
  • Some of the papers you have retrieved have suggested additional concepts or search terms

5. When to stop searching

There comes a point where the rewards of further searching may not be worth the the effort needed to capture additional references. The call to abort further searching depends on the question a review addresses and the resources that are available.  A thorough review of some high quality studies is generally preferable to a less discriminate probe for dubious items.  

Using custom built search filters

What is a custom built filter?  

Search filters ("hedges") are search strategies that have been devised and tested to filter the results of your search from large, general purpose databases including MEDLINE, EMBASE, and PsycINFO. These filters will improve the retrieval of scientifically sound and clinically relevant study reports, covering:

  • a specific clinical study category 
  • systematic reviews, meta-analyses, reviews of clinical trials, evidence-based medicine

Where are these filters available?

In PubMed, go to Clinical Queries, enter your search term and your results will be automatically categorised into Clinical Study Categories, Systematic Reviews and Medical Genetics. 

In Medline (Ovid), use the Additional Limits feature and then choose any of the nine categories in the Clinical Queries limit.