Utilitarianism: Is the root of the efficiency concept that lies in the notion that the good of society is served by achieving the greatest good for the greatest number.
The Pareto Standard, according to which social welfare is increased only to the degree that some individuals are made better off while no individuals are made worse off as a consequence.
Modified Pareto Standard, efficiency is enhanced as long as those who are made better off compensate all who are harmed, so that in the net no one is made worse off and some are made better off.
The Rawl's stipulated that only those changes working for the maximum advantage of the least-advantage count unambiguously as improvements in social welfare.