The following is the Royal Swedish Academy of Science's citation for Professor Amartya Sen for his contributions to welfare economics:
Amartya Sen has made several key contributions to the research on fundamental problems in welfare economics. His contributions range from axiomatic theory of social choice, over definitions of welfare and poverty indexes, to empirical studies of famine. They are tied closely together by a general interest in distributional issues and a particular interest in the most impoverished members of society. Sen has clarified the conditions which permit aggregation of individual values into collective decisions, and the conditions which permit rules for collective decision making that are consistent with a sphere of rights for the individual. By analyzing the available information about different individuals' welfare when collective decisions are made, he has improved the theoretical foundation for comparing different distributions of society's welfare and defined new, and more satisfactory, indexes of poverty. In empirical studies, Sen's applications of his theoretical approach have enhanced our understanding of the economic mechanisms underlying famines.
Can the values which individual members of society attach to different alternatives be aggregated into values for society as a whole, in a way that is both fair and theoretically sound? Is the majority principle a workable decision rule? How should income inequality be measured? When and how can we compare the distribution of welfare in different societies? How should we best determine whether poverty is on the decline? What are the factors that trigger famines? By answering questions such as these, Amartya Sen has made a number of noteworthy contributions to central fields of economic science and opened up new fields of study for subsequent generations of researchers. By combining tools from economics and philosophy, he has restored an ethical dimension to the discussion of vital economic problems.
Individual values and collective decisions
When there is general agreement, the choices made by society are uncontroversial. When opinions differ, the problem is to find methods for bringing together different opinions in decisions which concern everyone. The theory of social choice is preoccupied precisely with this link between individual values and collective choice. Fundamental questions are whether - and, if so, in what way - preferences for society as a whole can be consistently derived from the preferences of its members. The answers are crucial for the feasibility of ranking, or otherwise evaluating, different social states and thereby constructing meaningful measures of social welfare.
Majority rule
Majority voting is perhaps the most common rule for making collective decisions. A long time ago, this rule was found to have serious deficiencies, in addition to the fact that it may allow a majority to suppress a minority. In some situations it may pay off to vote strategically (i.e. by not voting for the preferred alternative), or to manipulate the order in which different alternatives are voted upon. Voting between pairs of alternatives sometimes fails to produce a clear result in a group. A majority may thus prefer alternative a to alternative b whereas a (second) majority prefers b to c ; meanwhile, a (third) majority prefers c to a. In the wake of this kind of "intransitivity", the decision rule cannot select an alternative that is unambiguously best for any majority. In collaboration with Prasanta Pattanaik, Amartya Sen has specified the general conditions that eliminate intransitivities of majority rule.
In the early 1950s, such problems associated with rules for collective choice motivated economics laureate Kenneth Arrow (1972) to examine possible rules for aggregating individual preferences (values, votes), where majority rule was only one of many alternatives. His surprising but fundamental result was that no aggregation (decision) rule exists that fulfills five conditions (axioms), each of which appears very reasonable on its own.
This so-called impossibility theorem seemed to be an insurmountable obstacle to progress in the normative branch of economics for a long time. How could individual preferences be aggregated and different social states evaluated in a theoretically satisfactory way? Sen's contributions from the mid-1960s onwards were instrumental in alleviating this pessimism. His work not only enriched the principles of social choice theory; they also opened up new and important fields of study. Sen's monograph Collective Choice and Social Welfare from 1970 was particularly influential and inspired many researchers to renew their interest in basic welfare issues. Its style, interspersing formally and philosophically oriented chapters, gave the economic analysis of normative problems a new dimension. In the book as well as many separate articles, Sen treated problems such as: majority rule, individual rights, and the availability of information about individual welfare.
Individual rights
A self-evident prerequisite for a collective decision-making rule is that it should be "non-dictatorial"; that is, it should not reflect the values of any single individual. A minimal requirement for protecting individual rights is that the rule should respect the individual preferences of at least some people in at least some dimension, for instance regarding their personal sphere. Sen pointed to a fundamental dilemma by showing that no collective decision rule can fulfill such a minimal requirement on individual rights and the other axioms in Arrow's impossibility theorem. This finding initiated an extensive scientific discussion about the extent to which a collective decision rule can be made consistent with a sphere of individual rights.
Information about the welfare of individuals
Traditionally, the theory of social choice had only assumed that every individual can rank different alternatives, without assuming anything about interpersonal comparability. This assumption certainly avoided the difficult question of whether the utility individuals attach to different alternatives can really be compared. Unfortunately, it also precluded saying anything worthwhile about inequality. Sen initiated an entirely new field in the theory of social choice, by showing how different assumptions regarding interpersonal comparability affect the possibility of finding a consistent, non-dictatorial rule for collective decisions.
Indexes of welfare and poverty
In order to compare distributions of welfare in different countries, or to study changes in the distribution within a given country, some kind of index is required that measures differences in welfare or income. The construction of such indexes is an important application of the theory of social choice, in the sense that inequality indexes are closely linked to welfare functions representing the values of society. Serge Kolm, Anthony Atkinson and - somewhat later - Amartya Sen were the first to derive substantial results in this area. Around 1970, they clarified the relation between the so-called Lorentz curve (that describes the income distribution), the so-called Gini coefficient (that measures the degree of income inequality), and society's ordering of different income distributions. Sen has later made valuable contributions by defining poverty indexes and other welfare indicators.
Poverty indexes
A common measure of poverty in a society is the share of the population, H , with incomes below a certain, predetermined, poverty line. But the theoretical foundation for this kind of measure was unclear. It also ignored the degree of poverty among the poor; even a significant boost in the income of the poorest groups in society does not affect H as long as their incomes do not cross the poverty line. To remedy these deficiencies, Sen postulated five reasonable axioms from which he derived a poverty index: P = H
