Earlier quoted context omitted.
How about median valuation?
The trouble with median valuation is that even for the most successful incubators it will approach zero, because I doubt any of us are going to have a success rate over 50%.
One huge winner could randomly happen in an otherwise low-quality program and that incubator would appear higher on rankings forever after that unjustly since the result is very much not reproducible. In other words measuring by average could mask getting lucky.