A concept due to the Italian economist and social theorist Vilfredo Pareto (1848-1923)

A social state is said to be Pareto efficient when there is no feasible alternative to it in which at least one individual is better off and no individual is worse off. That is to say:

Given two possible states of affairs (e.g., distributions of resources) S1 and S2, S2 is Pareto efficient with respect to S1 (or “Pareto superior”) if no one prefers S1 to S2 and at least one person prefers S2 to S1.

• When a competitive market reaches equilibrium, the outcome can be described as a Pareto optimum in that there are no Pareto efficient moves left: i.e., there are no remaining ways of redistributing holdings (or whatever else can be distributed) that would make someone better off without making someone else worse off. To put that another way: State S is Pareto optimal if there exists no State S₁ that is Pareto superior to it.
  
  
• One of the problems with utilitarianism, you will recall, was the problem of finding a common measure for interpersonal comparisons of utility. Pareto developed this sort of analysis to overcome such problems. We cannot make interpersonal comparisons of utility, says Pareto, but each person can judge for herself whether she is better off in S1 or S2. So, if everyone prefers S2 to S1, we have reason to believe that general social welfare must be greater in S2.

简言之就是：如果唯一增加某人福利的方法就是牺牲其他人的福利，那么这种状态下就是具有帕累托效率的，也就是我们西方经济学上一般所谓的“最有效的”。

这是周期帖了。可与下面并贴讨论。

https://bbs.pinggu.org/dispbbs.asp?BoardID=47&replyID=346582&id=55400&skin=0

https://bbs.pinggu.org/dispbbs.asp?BoardID=47&replyID=277467&id=45803&skin=0

https://bbs.pinggu.org/dispbbs.asp?BoardID=47&replyID=81778&id=13912&skin=0

不存在“强帕累托改善”（可能性）的状态是“强帕累托效率”状态。

但不存在“弱帕累托改善”（可能性）的状态不是“弱帕累托效率”状态（而是一种“更强的”帕累托效率状态）。所有资源只归一个人所有也是一种帕累托效率状态。

理解“帕累托效率”要从“帕累托改善”入手。不存在“越弱的”帕累托改善，则是“越强的”帕累托效率；反之，不存在“越强的”帕累托改善，则是“越弱的”帕累托效率。