The snowballing technique involves two approaches.  First, you scour the references sections of articles that you have already included in the review.   Second, you can use certain citation tracking databases to identify articles that had subsequently cited papers that you have included in the review.  The first approach works back in time from the article, whilst the second approach works forward in time from that article. 

Some databases allow you to undertake this process electronically.  The following example shows a paper on systematic review published in the British Journal of Management in 2003.  The search was performed in the ISI Web of Knowledge database.  You can see that this article references 75 texts.  Since publication in 2003 this paper has been cited by 48 papers in the ISI Web of Knowledge database. 

You will also see that there is an option to produce a citation map.  This is a graphical representation of the reference tracking and citation tracking:

You should perform both reference tracking and citation tracking for every article that you deem relevant for the review.  Make a list of the articles that you find by snowballing and include this table in your protocol/plan.

List of articles	Number of papers
Located through reference tracking:
1. 2. n.
Located through citation tracking:
1. 2. n.
Total number of articles located through snowballing

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