Nice tool here courtesy Microsoft
What is Erdos Number
The Erdős number (Hungarian pronunciation: [ˈɛrdøːʃ]) describes the “collaborative distance” between a person and mathematician Paul Erdős, as measured by authorship of mathematical papers.
The same principle has been proposed for other eminent people in other fields.
http://academic.research.microsoft.com/VisualExplorer#486937&1112639
Here are two of them-
you can see how prolific Hadley and Ripley are
http://academic.research.microsoft.com/Author/2867732/hadley-wickham
DECISION STATS 