What really strikes me about this data set is that YCombinator alone has 2x the exits of all the other other accelerators combined, and accounts for 93% of the total exit amount. Whenever someone asks "why you choose YC?" just quote that - its no guarantee of success by any means but I am certainly happy to keep such good company.
I should note the author things the exit value numbers for this study are bogus, so that that stat as an indicator not necessarily a piece of data.