In America's National Football League, a player gets full credit only for a so-called sack when he alone brings down the quarterback. In the world of US patents, a patent holder rakes in all the royalties if he or she is the sole name on the invention. If there's more than one name, the money is equally shared. It's called Laplace's Principle of Insufficient Reason: Without grounds for specifying unequal portions, the rational approach is to apportion equally. And it is, I'm convinced, the method by which scientists should calculate their citation numbers.