Advantages of using existing data:

• The cost and time demands of gathering existing information are generally low.
• You may find high-quality data, gathered in a sound way by experts, covering a much larger geographical area or sample size than you could have tackled yourself.
• The data may have been collected at different points in time, so you can use it to establish a baseline and discern a trend.
• The data could be broken down in such a way that you can easily supplement it with additional evidence of your own.

Source: CAFOD, Christian Aid and Trocaire (2007) Monitoring Government Policies: A toolkit for civil rights organisations in Africa: p.50.