Welfare economics typically takes individual preferences as given and stipulates a welfare improvement in Pareto efficiency terms from social state A to social state B if at least one person prefers B and no one else opposes it. There is no requirement of a unique quantitative measure of the welfare improvement implied by this. Another aspect of welfare treats income/goods distribution, including equality, as a further dimension of welfare.
Social welfare refers to the overall welfare of society. With sufficiently strong assumptions, it can be specified as the summation of the welfare of all the individuals in the society. Welfare may be measured either cardinally in terms of "utils" or dollars, or measured ordinally in terms of Pareto efficiency. The cardinal method in "utils" is seldom used in pure theory today because of aggregation problems that make the meaning of the method doubtful, except on widely challenged underlying assumptions. In applied welfare economics, such as in cost-benefit analysis, money-value estimates are often used, particularly where income-distribution effects are factored into the analysis or seem unlikely to undercut the analysis.
The capabilities approach to welfare argues that freedom - what people are free to do or be - should be included in welfare assessments, and the approach has been particularly influential in development policy circles where the emphasis on multi-dimensionality and freedom has shaped the evolution of the Human Development Index.
Other classifying terms or problems in welfare economics include externalities, equity, justice, inequality, and altruism.
 Two approachesThere are two mainstream approaches to welfare economics: the early Neoclassical approach and the New welfare economics approach.
The early Neoclassical approach was developed by Edgeworth, Sidgwick, Marshall, and Pigou. It assumes the following:
- Utility is cardinal, that is, scale-measurable by observation or judgment.
- Preferences are exogenously given and stable.
- Additional consumption provides smaller and smaller increases in utility (diminishing marginal utility).
- All individuals have interpersonally comparable utility functions (an assumption that Edgeworth avoided in his Mathematical 'Psychics).
The New Welfare Economics approach is based on the work of Pareto, Hicks, and Kaldor. It explicitly recognizes the differences between the efficiency aspect of the discipline and the distribution aspect and treats them differently. Questions of efficiency are assessed with criteria such as Pareto efficiency and the Kaldor-Hicks compensation tests, while questions of income distribution are covered in social welfare function specification. Further, efficiency dispenses with cardinal measures of utility, replacing it with ordinal utility, which merely ranks commodity bundles (with an indifference-curve map, for example).
 EfficiencySituations are considered to have distributive efficiency when goods are distributed to the people who can gain the most utility from them.
Many economists use Pareto efficiency as their efficiency goal. According to this measure of social welfare, a situation is optimal only if no individuals can be made better off without making someone else worse off.
This ideal state of affairs can only come about if four criteria are met:
- The marginal rates of substitution in consumption are identical for all consumers. This occurs when no consumer can be made better off without making others worse off.
- The marginal rate of transformation in production is identical for all products. This occurs when it is impossible to increase the production of any good without reducing the production of other goods.
- The marginal resource cost is equal to the marginal revenue product for all production processes. This takes place when marginal physical product of a factor must be the same for all firms producing a good.
- The marginal rates of substitution in consumption are equal to the marginal rates of transformation in production, such as where production processes must match consumer wants.
- Imperfect market structures, such as a monopoly, monopsony, oligopoly, oligopsony, and monopolistic competition.
- Factor allocation inefficiencies in production theory basics.
- Market failures and externalities; there is also social cost.
- Price discrimination and price skimming.
- Asymmetric information, principal–agent problems.
- Long run declining average costs in a natural monopoly.
- Certain types of taxes and tariffs.
See also: first welfare theorem
 Income distributionThere are many combinations of consumer utility, production mixes, and factor input combinations consistent with efficiency. In fact, there are an infinity of consumption and production equilibria that yield Pareto optimal results. There are as many optima as there are points on the aggregate production possibilities frontier. Hence, Pareto efficiency is a necessary, but not a sufficient condition for social welfare. Each Pareto optimum corresponds to a different income distribution in the economy. Some may involve great inequalities of income. So how do we decide which Pareto optimum is most desirable? This decision is made, either tacitly or overtly, when we specify the social welfare function. This function embodies value judgements about interpersonal utility. The social welfare function shows the relative importance of the individuals that comprise society.
A utilitarian welfare function (also called a Benthamite welfare function) sums the utility of each individual in order to obtain society's overall welfare. All people are treated the same, regardless of their initial level of utility. One extra unit of utility for a starving person is not seen to be of any greater value than an extra unit of utility for a millionaire. At the other extreme is the Max-Min, or Rawlsian utility function (Stiglitz, 2000, p102)[incomplete reference]. According to the Max-Min criterion, welfare is maximized when the utility of those society members that have the least is the greatest. No economic activity will increase social welfare unless it improves the position of the society member that is the worst off. Most economists specify social welfare functions that are intermediate between these two extremes.
The social welfare function is typically translated into social indifference curves so that they can be used in the same graphic space as the other functions that they interact with. A utilitarian social indifference curve is linear and downward sloping to the right. The Max-Min social indifference curve takes the shape of two straight lines joined so as they form a 90 degree angle. A social indifference curve drawn from an intermediate social welfare function is a curve that slopes downward to the right.
A crude social welfare function can be constructed by measuring the subjective dollar value of goods and services distributed to participants in the economy (see also consumer surplus).
 A simplified seven-equation modelThe basic welfare economics problem is to find the theoretical maximum of a social welfare function, subject to various constraints such as the state of technology in production, available natural resources, national infrastructure, and behavioural constraints such as consumer utility maximization and producer profit maximization. In the simplest possible economy this can be done by simultaneously solving seven equations. This simple economy would have only two consumers (consumer 1 and consumer 2), only two products (product X and product Y), and only two factors of production going into these products (labour (L) and capital (K)). The model can be stated as:
- maximize social welfare: W=f(U1 U2) subject to the following set of constraints:
- K = Kx + Ky (The amount of capital used in the production of goods X and Y)
- L = Lx + Ly (The amount of labour used in the production of goods X and Y)
- X = X(Kx Lx) (The production function for product X)
- Y = Y(Ky Ly) (The production function for product Y)
- U1 = U1(X1 Y1) (The preferences of consumer 1)
- U2 = U2(X2 Y2) (The preferences of consumer 2)
Also, finding a solution to an abstract function does not directly yield a policy recommendation! In other words, solving an equation does not solve social problems. However, a model like the one above can be viewed as an argument that solving a social problem (like achieving a Pareto-optimal distribution of wealth) is at least theoretically possible.
 Efficiency between production and consumptionThe relation between production and consumption in a simple seven equation model (2x2x2 model) can be shown graphically. In the diagram below, the aggregate production possibility frontier, labeled PQ shows all the points of efficiency in the production of goods X and Y. If the economy produces the mix of good X and Y shown at point A, then the marginal rate of transformation (MRT), X for Y, is equal to 3.
Edgeworth box diagram of consumption. That is, the same mix of products that are produced at point A, can be consumed by the two consumers in this simple economy. The consumers' relative preferences are shown by the indifference curves inside the Edgeworth box. At point B the marginal rate of substitution (MRS) is equal to 2, while at point C the marginal rate of substitution is equal to 3. Only at point B is consumption in balance with production (MRS=MRT). The curve 0BCA (often called the contract curve) inside the Edgeworth box defines the locus of points of efficiency in consumption (MRS1=MRS ²). As we move along the curve, we are changing the mix of goods X and Y that individuals 1 and 2 choose to consume. The utility data associated with each point on this curve can be used to create utility functions.
 Social welfare maximizationUtility functions can be derived from the points on a contract curve. Numerous utility functions can be derived, one for each point on the production possibility frontier (PQ in the diagram above). A social utility frontier (also called a grand utility frontier) can be obtained from the outer envelope of all these utility functions. Each point on a social utility frontier represents an efficient allocation of an economy's resources; that is, it is a Pareto optimum in factor allocation, in production, in consumption, and in the interaction of production and consumption (supply and demand). In the diagram below, the curve MN is a social utility frontier. Point D corresponds with point C from the earlier diagram. Point D is on the social utility frontier because the marginal rate of substitution at point C is equal to the marginal rate of transformation at point A. Point E corresponds with point B in the previous diagram, and lies inside the social utility frontier (indicating inefficiency) because the MRS at point C is not equal to the MRT at point A.
 Welfare economics in relation to other subjectsWelfare economics uses many of the same techniques as microeconomics and can be seen as intermediate or advanced microeconomic theory. Its results are applicable to macroeconomic issues so welfare economics is somewhat of a bridge between the two branches of economics.
Cost-benefit analysis is a specific application of welfare economics techniques, but excludes the income distribution aspects.
Political science also looks into the issue of social welfare (political science), but in a less quantitative manner.
Human development theory explores these issues also, and considers them fundamental to the development process itself.
 Paretian welfare economicsParetian welfare economics rests on the assumed value judgment that, if a particular change in the economy leaves at least one individual better off and no individual worse off, social welfare may be said to have increased.
 CriticismsSome, such as economists in the tradition of the Austrian School, doubt whether a cardinal utility function, or cardinal social welfare function, is of any value. The reason given is that it is difficult to aggregate the utilities of various people that have differing marginal utility of money, such as the wealthy and the poor.
Also, the economists of the Austrian School question the relevance of pareto optimal allocation considering situations where the framework of means and ends is not perfectly known, since neoclassical theory always assumes that the ends-means framework is perfectly defined.
Some even question the value of ordinal utility functions. They have proposed other means of measuring well-being as an alternative to price indices, "willingness to pay" functions, and other price oriented measures. These price based measures are seen as promoting consumerism and productivism by many. It should be noted that it is possible to do welfare economics without the use of prices, however this is not always done.
Value assumptions explicit in the social welfare function used and implicit in the efficiency criterion chosen tend to make welfare economics a normative and perhaps subjective field. This can make it controversial.
However, perhaps most significant of all are concerns about the limits of a utilitarian approach to welfare economics. According to this line of argument utility is not the only thing that matters and so a comprehensive approach to welfare economics should include other factors. The capabilities approach to welfare is an attempt to construct a more comprehensive approach to welfare economics, one in which functionings, happiness and capabilities are the three key aspects of welfare outcomes that people should seek to promote and foster.
 See also
- Deardorff's Glossary of International Economics (2006). "Welfare economics."
- I.M.D. Little, A Critique of Welfare Economics (1950). There are many such proposed measures of welfare, including the Theil index and those in Amartya Sen On Economic Inequality, Annexe with James E. Foster (1997), Clarendon Press, Oxford, ISBN 0-19-828193-5.
- Arrow, Kenneth J. (1951, 2nd ed., 1963). Social Choice and Individual Values, Yale University Press, New Haven.
- Arrow, Kenneth J., and Gérard Debreu ed., 2002. Landmark Papers in General Equilibrium Theory, Social Choice and Welfare. Edward Elgar Publishing, ISBN 978-1-84064-569-9. Description and table of contents.
- Atkinson,Anthony B. (1975). The Economics of Inequality, Oxford University Press, London.
- Bator, Francis M. (1957). "The Simple Analytics of Welfare Maximization," American Economic Review, 47(1), p p. 22-59.
- Calsamiglia, Xavier, and Alan Kirman (1993). "A Unique Informationally Efficient and Decentralized Mechanism with Fair Outcomes," Econometrica, 61(5), p p. 1147-1172.
- Chipman, John S., and James C. Moore (1978). "The New Welfare Economics 1939-1974," International Economic Review, 19(3), p p. 547-584.
- Mishan, E. J. (1980). "The New Welfare Economics: An Alternative View," International Economic Review, 21(3), p p. 691-705.
- Feldman, Allan M. (1987). "equity," The New Palgrave: A Dictionary of Economics, v. 2, pp. 183–84.
- _____ (1987 ). "welfare economics," The New Palgrave: A Dictionary of Economics, v. 4, pp. 889–95. Abstract.
- Feldman, Allan M., and Roberto Serrano,  2006. Welfare Economics and Social Choice Theory, 2nd ed. ISBN 0-387-29367-1, ISBN 978-0-387-29367-7 Arrow-serachable chapter previews.
- Graaff, Johannes de Villiers, (1957; rev. ed., 1968). Theoretical Welfare Economics, ISBN 978-0-521-09446-7 Cambridge, UK: Cambridge University Press.
- Harberger, Arnold C. (1971) "Three Basic Postulates for Applied Welfare Economics: An Interpretive Essay," Journal of Economic Literature, 9(3), p p. 785-797.
- Just, Richard et al. (2004), The Welfare Economics of Public Policy, Edward Elgar Publishing, Cheltenham and Northampton.
- Kuenne, Robert E., ed. (2000), Readings in Social Welfare: Theory and Policy, Wiley. Description and scroll to chapter-preview links.
- Little, I.M.D. (1950; 2002). A Critique of Welfare Economics, Oxford. Preview. ISBN 0-19-828119-6.
- Ng, Yew-Kwang (1979; rev. ed., 1983). Welfare economics. London: Macmillan.
- O'Connell, John F. (1982) Welfare Economic Theory, Auburn House Publishing, Boston.
- Samuelson, Paul A. (1947, Enlarged ed. 1983). "Welfare Economics," Foundations of Economic Analysis, Harvard University Press, Cambridge, MA, ch. VIII, pp. 203–53.
- _____ (1977). "Reaffirming the Existence of 'Reasonable' Bergson-Samuelson Social Welfare Functions," Economica, N.S., 44(173), p p. 81-88. Reprinted in (1986) The Collected Scientific Papers of Paul A. Samuelson, pp. 47-54.
- _____ (1981). "Bergsonian Welfare Economics", in S. Rosefielde (ed.), Economic Welfare and the Economics of Soviet Socialism: Essays in Honor of Abram Bergson, Cambridge University Press, Cambridge, pp. 223–66. Reprinted in (1986) The Collected Scientific Papers of Paul A. Samuelson, pp. 3 -46.
- Sen, Amartya K. (1963). "Distribution, Transitivity and Little's Welfare Criteria," Economic Journal, 73(292), p. 771-78.
- _____ (1982). Choice, Welfare and Measurement, MIT Press. Description and scroll to chapter-preview links.
- Suzumura, Kotaro (1980). "On Distributional Value Judgments and Piecemeal Welfare Criteria," Economica, 47(186), p p. 125-39.
- Sustainable National Income at wikinfo