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Systematic Reviews: Searching for evidence

Searching for evidence

Once you have formulated your research question and decided on the most appropriate protocol is for your research, the next step is to decide what information you need to find to answer your question and to decide where best to search for that information.

Taking the time to develop a search strategy will help you to answer these questions and to ensure your search is approached in a methodical, consistent and structured manner. Being methodical is important as, ideally, your systematic review aims to find all the literature that is relevant to your research topic. Taking a structured approach to searching for this evidence will assist in this objective.

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Systematic reviews

Searching for systematic reviews

The first stage in your search is to locate systematic reviews that have already been undertaken on your topic of interest. You should do this for a number of reasons: 

  • To ensure your question has not already been answered by others
  • To check there are no protocols of reviews registered that are also looking to answer the same research question
  • To locate related systematic reviews that are based on your topic so you can access their reference lists to determine the primary studies they included.

Where to search for systematic reviews?

There are a number of databases and websites that you can use to find systematic reviews:

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For more information on using Cochrane library, click here

Searching for primary studies

When conducting a systematic review, you want to find the highest level of evidence - referring back to the EBM pyramid these are systematic reviews and meta-analyses. However, there may be a need to search for types of studies that have produced original data, ideas or information. In these circumstances, you should work down to the next highest level of evidence.

Developing a search strategy, will allow you to effectively search and find relevant primary studies. The library contains online resources that will assist you in your search:

Academic databases contain many different types of studies. Some databases focus on a specific discipline(s) while others are multidisciplinary. The Databases A-Z comprises of a complete list of databases accessible at QMU. The subject library guides will help to identify the most relevant databases for your research area, as well as including instruction on using databases.

Primary studies are often published in academic journals. The E-Journals A-Z will help you to identify what titles QMU has electronic access to.

Grey literature

What is Grey Literature?

The Fourth International Conference on Grey Literature (GL '99) in Washington, DC, in October 1999 defined grey literature as: "That which is produced on all levels of government, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers."

Therefore, grey literature is published, or unpublished, literature that has been made available through means other than traditional publishing routes, such as in published books or journals.

More information about grey literature

More information about grey literature, and why it should be included, can be found in the Grey Literature libguide.

Video - Searching the Literature for Your Systematic Review

Presented by Laurie Theeke, Ph.D. WVU School of Nursing Lecture 3 

Additional techniques for retrieving information

Citation searching 

You may also wish to include citation searching in your protocol to complement your search strategy. You can employ citation searching once you have found key or seminal papers that are focused on the subject area you are interested in.

You can use these papers as your base to:
•    track how an idea has developed over time
•    find other current, high-quality papers focused on the subject area of interest
•    Identify other authors that might have cited the papers you have identified
•    Help broaden the parameters of your search strategy

It is important to remember this type of search should not be carried out in isolation but as part of a systematic, exhaustive search strategy to avoid any bias (see Developing the review protocol tab for more information on avoiding bias).

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Backward citation searching

Backward citation searching (also known as ‘bibliographic mining’ or ‘cited reference searching’) looks backwards in time, examining selected papers’ reference lists, to help identify authors prevalent in the field and to develop a better understanding of how the topic of interest has developed over time.

How to do it

After scanning the reference list of your chosen paper, take the details of any articles or authors that might be of interest. You can then use QMU’s library catalogue, E-Journals A-Z list, QMU’s academic databases (all found in your subject libguide) or search engines, such as Google Scholar, to search for specific articles or works by a particular author.

In some academic databases, such as Web of Science or Scopus, they will include a link to the references, or will list the references in the citation record of the article.

Forward citation searching

As the name suggests, this type of search requires you to look forwards in time. By identifying what articles have cited the paper you are interested in, this information can help you to assess the importance of that paper to the development of the discipline/field of interest.

As with backward citation searching, you can search for articles that have cited the work you are looking at, or search for a particular author.

How to do it

More databases are including information for users about who has cited a particular article.  Look for a database with a citation index, such Web of Science, ScienceDirect, Scopus and the search engine Google Scholar. The following examples are for Web of Science and Scopus

Web of Science 

  • Go to Web of Science
  • Select "Cited Reference Search"
  • Enter the details of the work you are interested (such as the author)

  • Web of Science will generate a list based on the information you have entered
  • Check the entries that are relevant to your search and then select 'Finish Search'



  • Search for the title or author of the work of interest
  • From the results, check the left-hand box to select the work you are interested in
  • Then click on the "View cited by" option

  • You will be presented with a list of of the papers, indexed within Scopus, that cited the work of interest

What is handsearching?

Handsearching involves the researcher manual scanning (cover-by-cover, page-by-page) material that has been selected specifically. Cochrane Library, when considering searching for controlled trials, defines handsearching as “…the task of searching through medical journals or conference publications for reports of controlled trials which are not indexed in the major electronic databases” (section 5 Handsearching). This definition can be applied, however, to searching for any material type within any discipline.

The search can involve you searching (either within online or print format), for example, the table of contents of a specific journal issue or conference proceeding, or systematically searching through  a website for relevant guides, policy documents or reports.  

Why should you consider include handsearching in your protocol?

Although employing a comprehensive strategy to search appropriate academic databases is a vital component of the review, there are instances where potentially relevant material might still be missed. This can occur due to:

  • Some databases so not index their items comprehensively. Therefore, there is a risk that some relevant material might be missed. 
  • There is the possibility that the search strategy may not comprehensive enough to identify all relevant material.
  • Some sources (such as material produced by companies/organisations) are traditionally not included in academic databases

In addition, handsearching allows you to conduct a more detailed scanning of key sources.

Forward and backward citation searching 

A video tutorial from the University of Wisconsin

Web of Science: How to do a Cited Reference Search

Web of Science tutorial looking at how to search for citations to journal articles, books, and more with Cited Reference searching.