Well, on a long enough time span, all companies die. Picking the number of years afterward to measure by is tough and may not be the best way to do so. Perhaps measuring the success by a more personal and human method describes the elephant better: Deferred income. Take an average (yes, also fraught with trouble) of yearly income for people of that skill set (entrepuners, coders, widget makers, inventors, etc ) and then see if the founders and employees made less, within a standard deviation, or far above that average, on a year to year basis. This is really troublesome to get the data at all, as it is very personal and emotional to a lot of folk. Also, the average is pretty wonky here as well. However, it should be a starting point to see how companies are doing a little bit better than a plain up/down number.