Optimal Apportionment Yukio Koriyama∗, Jean-François Laslier,

This paper provides a theoretical foundation which supports the degressive proportionality principle in apportionment problems. The core of the argument is that each individual derives utility from the fact that the collective decision matches her own will with some frequency, with marginal utility decreasing with respect to this frequency. Then classical utilitarianism at the social level recommends decision rules which exhibit degressive proportionality. The model is applied to the case of the 27 states of the European Union