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Stony Brook University

Systematic Reviews: Additional Searching

A guide to conducting systematic reviews.


Snowballing is the process of

  • citation tracking from one article to another
  • using the reference lists of selected articles to locate other articles of importance (backtracking)
  • seeing who cited a selected article to locate other articles of importance (forward tracking)

Why do it?

  • Locate old articles of importance that might predate online literature databases or not be indexed in them
  • Locate newer literature
  • Gain a sense of the history and relationships of the literature on the topic
  • Identify the authors who publish the most on the topic (the experts)

How to do it.

The most useful databases for reviewing cited articles and citing articles (citation tracking both backwards and forwards in time) are"

  1. Science Citation Index Expanded (Web of Science)


Handsearching is the process of

  • selecting journals of topical interest to the review question
  • looking through the issues (at least TOCs) of these selected journals ‘by hand’ to identify possibly-missed studies

It is traditionally done with print, but can be done electronically (see for additional information)

Why do it?

  • Some journals are not indexed in major literature databases
  • Journal supplements, news, editorials, letters, etc. may not be well indexed

Many journals contain conference proceedings that may not be well indexed

Author Contacts

One final step in high-quality systematic reviews is to contact the authors who are known to be important researchers in your topic area and ask if they have any unpublished studies or data that they would be willing to share. This may also include contacting pharmaceutical or medical device corporations to try to get study data that they have not released.