A controversial issue in welfare economics, interpersonal comparisons of utility are supposed to be avoided, according to common practice in 20th century economic theory. The idea is that if economics is to live up to the ideal of being a science, in the strict, positivist fashion, then economists must accept that they cannot look inside someone's mind to determine how much enjoyment they have.

In practice, this means one cannot say that a hungry leper is worse off than Bill Gates. Economists who wish to make normative judgments about economic systems or situations are therefore limited to such comparisons as Pareto efficiency.

This makes for great difficulties in Social Choice theory, which must either violate this dogma, or be extremely limited in constructing social welfare functions.