Nobel Prize in Economics 2015: Angus Deaton on Consumption Poverty and Welfare

This note covers the Nobel Prize in Economics 2015: who won it, why Angus Deaton's work on consumption, poverty and welfare mattered, how his research on demand systems, saving and household surveys developed over several decades, why it still matters for development policy, and quick facts for exams.

What was the Nobel Prize in Economics 2015 awarded for?

The Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel for 2015 was awarded "for his analysis of consumption, poverty, and welfare". This is the full official citation, and it was given entirely to one economist, Angus Deaton.

In plain words, the prize honours someone who spent decades studying a very ordinary question with huge consequences: how do people, especially poor people, decide what to buy and how much to save, and how can researchers measure whether their living standards are actually getting better or worse? The Royal Swedish Academy of Sciences said his work "helped transform the fields of microeconomics, macroeconomics, and development economics" by connecting what individual households choose to do with what happens in the economy as a whole.

The prize is widely called the Nobel Prize in Economics, though it is formally a Swedish central bank prize given "in memory of" Alfred Nobel rather than one of the five prizes Nobel's own will created.

It is announced by the Royal Swedish Academy of Sciences, usually in October, and handed over in Stockholm each December along with the other prizes.

Who is the laureate?

Angus Deaton: a life in applied economics

Angus Deaton was born on 19 October 1945 in Edinburgh, Scotland. He was educated at Fettes College and then studied at the University of Cambridge, where he completed his PhD in 1974.

He later taught at the University of Bristol before joining Princeton University in the United States in 1983, where he was Professor of Economics and International Affairs and remained affiliated at the time of the award.

He received the whole prize (a share of 1/1), worth 8,000,000 Swedish kronor. He holds both UK and US citizenship. The Nobel sources note he is married to the economist Anne Case and has one son and one daughter.

Deaton's contribution spanned three connected areas: building better tools to study how households split their spending across different goods, showing why studying individuals rather than national averages is essential to understanding saving and consumption over time, and pioneering the use of detailed household surveys to measure poverty and welfare in developing countries. Each strand is explained in its own section below.

What problem was Deaton trying to solve?

Before Deaton's work, economists who wanted to understand how people spend their money relied on fairly rigid mathematical models of "demand", and on national-level averages for income and spending.

These models assumed that a whole country's consumers behaved like one single, perfectly rational representative consumer.

When researchers tested this assumption against real data from the 1960s and 1970s, the results clashed with the theory, which seemed to suggest that ordinary people were not rational at all.

Deaton's early insight, developed in papers around 1974, was that this conclusion was too hasty.

He argued that the models themselves, not necessarily the consumers, might be at fault: they imposed assumptions on behaviour that were far too restrictive to match the real complexity of how households choose between food, clothes and other goods.

A second problem concerned poverty in developing countries. Governments and aid agencies needed to know how many people were poor and whether poverty was rising or falling, but poor households often have no steady recorded wages and live partly through subsistence farming and bartering, leaving few traces in official income statistics.

Deaton's later career addressed this gap by turning to detailed household consumption surveys instead of national income figures.

How do consumers decide what to buy?

A demand system is simply a set of equations, one for each type of good (food, clothing and so on), showing how much of that good people buy depending on its price, the prices of everything else, and their total income.

Governments need reliable demand systems to judge how a change in a tax, such as VAT on food, will affect different groups of people.

Around 1980, together with John Muellbauer, Deaton developed the Almost Ideal Demand System (AID System). It was built to be flexible enough to realistically describe spending patterns, yet simple enough to estimate from real data, and able to be tested against the three properties economic theory expects of rational behaviour.

The broad logic of building and using such a system runs through several steps:

1. Collect data on the prices of different goods and on how much households spend on each good.
2. Write an equation for each good showing its budget share as a function of all prices and of total household spending.
3. Check whether the fitted equations are consistent with the basic properties a rational consumer's choices should have, such as not being fooled by a proportional rise in all prices and income together.
4. Use the estimated system to predict how a proposed policy change, such as a new tax, would alter spending patterns and welfare for different income groups.

The Academy noted that after thirty-five years the AID System, and later refinements of it, remained standard tools for studying tax reforms, building price indexes, and comparing living standards across countries.

Draw a horizontal axis for total household spending and a vertical axis for the share of spending going on one good, such as food.

Sketch a downward-curving line showing that as households get richer, the share spent on food falls, which is the kind of pattern a flexible demand system like the AID System is built to capture.

How does income over time affect spending and saving?

A separate puzzle concerns how people decide to split income between spending now and saving for later.

Two famous theories from the 1950s, Milton Friedman's Permanent Income Hypothesis and Franco Modigliani's Life-Cycle Model, both predicted that people try to keep their consumption steady over time rather than letting it jump around with every change in income.

In papers around 1990, Deaton tested this theory using aggregate (whole-country) data on income and consumption and found a striking contradiction.

The theory predicted that consumption should vary more than income, because a rise in income this year usually signals further rises are likely, so a rational saver should spend some of that expected future gain immediately.

Yet in real national data, consumption varied less than income, the opposite of the prediction. This mismatch became known as the Deaton Paradox.

Deaton's resolution was to point out that the theory was being tested on the wrong level of data.

Individual incomes fluctuate very differently from the national average: when some people's incomes rise, others fall, and these ups and downs largely cancel out once added together.

By studying how individual households adjust their own consumption to their own income, and only afterwards summing up the results, the predictions of the theory matched the observed patterns in national data far better.

This work also introduced the idea of a pseudo panel: since true long-running surveys of the same households are rare, Deaton showed how repeated surveys of different people from the same age group could be used to build a usable substitute.

This approach helped shift macroeconomics away from working only with national averages, towards building up results from individual behaviour.

How did Deaton change the study of poverty in developing countries?

In later decades Deaton turned his methods towards development economics. He argued that in poor countries, where people often lack steady recorded wages, consumption data collected through household surveys gives a far more reliable picture of living standards than income data drawn from national accounts.

His research uncovered several important pitfalls in measuring poverty. He showed that a child's reasonable share of household expenditure is roughly 30 to 40 percent of an adult's, so simply dividing household spending equally per person overstates poverty in households with children.

He also explained why revisions to the official international poverty line had, at one point, increased the measured global count of poor people by nearly half a billion.

Deaton used household data to examine the long-debated idea of a poverty trap, where low income causes low calorie intake, which in turn keeps income low.

He found that higher income does lead to people eating more, but the evidence did not support the idea that poor nutrition itself was the main cause of poverty, rather the reverse.

He also devised an indirect way to test for gender discrimination within families, by checking whether households with sons spend differently on adult goods such as clothing, tobacco or alcohol than households with daughters.

Using surveys from several developing countries, he did not find clear evidence of systematic discrimination under normal circumstances, though later research found such discrimination appearing when families faced hardship.

How did the discovery unfold?

Deaton's contributions were not a single breakthrough but a body of work built up over four decades, moving from questioning existing demand theory, to building new tools, to applying them to real poverty measurement.

Why does this prize matter today?

Deaton's demand-system tools are still used, decades later, by governments and international agencies to work out how tax changes, subsidies and price shifts will affect different groups of people, and to build price indexes that compare living costs across places and time.

His insight that individual-level data must be studied, rather than only national averages, pushed modern macroeconomics to pay close attention to how income and consumption vary across households, not just across countries.

His work on poverty measurement changed how researchers and institutions such as the World Bank design household surveys, with real consequences for how global poverty counts are produced.

The Academy described development economics as having become "a flourishing empirical research field" built on detailed household data rather than theory alone, a shift Deaton's research helped drive.

Open questions remain about how best to compare poverty and welfare across very different countries and time periods, since local prices, available goods and the quality of goods all differ, and Deaton's own research repeatedly highlighted these pitfalls rather than claiming to have solved them completely.

His broader legacy, as the Academy's popular science account put it, is the habit of building bridges between economic theory, real data, and the lives of the people that data describes.

How does this connect to what you study?

Deaton's work connects directly to basic ideas taught in school economics: demand (how much of a good people buy at different prices), consumer behaviour, and national income and its relationship to saving and investment.

The idea that a tax on a good changes how much of it people buy, and that this effect differs across income groups, is exactly the kind of question his demand systems were built to answer.

His poverty-measurement work also links to topics on development economics and human development indicators, where students learn that income alone is an imperfect measure of welfare, and that factors such as calorie intake, housing and access to services matter too.

Understanding why economists increasingly use household surveys rather than only national accounts gives useful context for any discussion of how poverty statistics are actually produced.

Quick facts for exams

The Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel for 2015, commonly called the Nobel Prize in Economics 2015, was awarded entirely to Angus Deaton of Princeton University, USA, "for his analysis of consumption, poverty, and welfare".

The award was announced on 12 October 2015 by the Royal Swedish Academy of Sciences and presented in Stockholm on 10 December 2015, carrying a prize amount of 8,000,000 Swedish kronor.

Deaton, born in Edinburgh, Scotland in 1945, was honoured for three connected achievements: the Almost Ideal Demand System he built with John Muellbauer around 1980, his research on how individual income and consumption link up over time, and his pioneering use of household surveys to measure poverty and welfare in developing countries.

Note: Source. The prize facts in this note are from the Nobel Prize's official site, nobelprize.org.

Glossary

• Demand system — a set of equations showing how much of each good consumers buy depending on prices and income.
• Almost Ideal Demand System (AID System) — the flexible demand model Deaton and Muellbauer introduced around 1980 to estimate consumer behaviour.
• Engel curve — a curve showing how the share of spending on a good changes as total household spending rises.
• Representative consumer — a simplifying assumption that treats a whole economy's consumers as if they were one average individual.
• Permanent Income Hypothesis — Milton Friedman's theory that people base spending on their expected long-run average income, not just current income.
• Life-Cycle Model — Franco Modigliani's related theory that people smooth spending across their whole lifetime, saving in working years and spending savings in retirement.
• Deaton Paradox — the puzzle that aggregate consumption varies less than the theory predicted, resolved by looking at individual rather than national income data.
• Pseudo panel — a substitute for true long-term survey data, built by tracking cohorts of similar people across repeated cross-sectional surveys.
• Household survey — detailed data collection asking individual households what they spend, eat and own, used to measure living standards.
• Poverty line — an income or expenditure level below which a person is counted as poor.
• Poverty trap — the idea that low income causes low calorie intake, which keeps income low, trapping people in poverty.
• Unit value — expenditure on a good divided by the quantity bought, used to estimate local prices when direct price data is missing.
• Liquidity constraint — a limit on a household's ability to borrow, which affects how it can smooth spending over time.
• Missing women — the term for the demographic gap caused by favouring sons over daughters in parts of the developing world.

Common errors and misconceptions

• Misconception: The Nobel Prize in Economics is one of the original prizes created by Alfred Nobel's will. Correct: It is a separate prize established by Sweden's central bank, awarded "in memory of" Alfred Nobel alongside the original prizes.
• Misconception: Deaton won the prize for a single discovery. Correct: The citation covers three connected contributions across decades: demand systems, consumption over time, and poverty measurement.
• Misconception: The Deaton Paradox means people's consumption is perfectly smooth and theory is wrong. Correct: It means the standard theory, tested on aggregate data, failed, and the puzzle was resolved by studying individual income and consumption instead.
• Misconception: Deaton's research proved malnutrition causes poverty. Correct: His evidence instead suggested low income causes poor nutrition, not the reverse, in the cases he studied.
• Misconception: Household surveys and national accounts always give the same poverty figures. Correct: Deaton showed the two can point in different directions, making careful choice of data crucial.
• Misconception: Per-person division of household spending gives an accurate poverty measure. Correct: Deaton showed this overstates poverty in households with children, since a child needs less than an adult.
• Misconception: Deaton worked alone throughout his career. Correct: The Almost Ideal Demand System was developed jointly with John Muellbauer, and other key papers were co-authored, for example with Blinder and with Campbell.

Exam-style questions with model answers

Q1. In which year was the Nobel Prize in Economics 2015 announced, and to whom was it awarded? [1 mark]

1. It was announced on 12 October 2015 and awarded entirely to Angus Deaton of Princeton University.

Q2. State the official citation for Angus Deaton's prize. [2 marks]

1. The citation reads "for his analysis of consumption, poverty, and welfare", covering his work on demand, saving over time, and poverty measurement.

Q3. Explain what the Almost Ideal Demand System is and why it was important. [4 marks]

1. The Almost Ideal Demand System is a set of equations, developed by Deaton and John Muellbauer around 1980, showing how much a household spends on each type of good depending on all prices and total expenditure.
2. Earlier demand models were too rigid to realistically match real spending patterns while also testing whether consumers behaved rationally.
3. The new system was flexible enough to fit real data yet simple enough to estimate, and it allowed economists to test the standard properties of rational demand.
4. It became a standard tool for evaluating tax reforms, building price indexes and comparing living standards, still widely used decades later.

Q4. What is the Deaton Paradox, and how did Deaton help resolve it? [4 marks]

1. Standard theory predicted that consumption should vary more than income, yet national data showed consumption varying less than income, a contradiction called the Deaton Paradox.
2. Deaton showed the problem lay in testing the theory on national averages rather than individuals.
3. Individual incomes rise and fall very differently from person to person, and these differences largely cancel out in national totals.
4. By studying how each household adjusts its own spending to its own income, and then summing the results, the theory's predictions matched real aggregate patterns far better.

Q5. Discuss how Angus Deaton's research changed the study of poverty in developing countries. [6 marks]

1. Before Deaton's work, development economics relied mainly on theory and on aggregate national-account data, which poorly captures the lives of people in informal, subsistence economies.
2. Deaton argued that consumption data collected directly from households gives a more reliable picture of welfare than income data in such settings, since poor households often lack steady recorded wages.
3. He showed that measuring poverty per person overstates the problem in households with children, since children typically need only about 30 to 40 percent of an adult's expenditure.
4. He identified important pitfalls in comparing poverty across time and place, including cases where national accounts and household surveys suggested opposite trends.
5. His research on income and calorie intake found that higher income raises calorie consumption, but that poor nutrition is largely a consequence of low income rather than its cause.
6. He also devised an indirect method using household spending on adult goods to test for gender discrimination between sons and daughters within families.
7. Together, these contributions helped shift development economics from a mainly theoretical field into an empirical field built on detailed household survey data.

Q6. Name the two theories from the 1950s that Deaton's work tested, and who proposed them. [2 marks]

1. These were Milton Friedman's Permanent Income Hypothesis and Franco Modigliani's Life-Cycle Model, both of which argued that people smooth consumption over time rather than letting it track income directly.

Q7. What is a pseudo panel, and why did Deaton develop this idea? [3 marks]

1. A pseudo panel is built from repeated cross-sectional surveys of different people from the same age cohort, used as a substitute when true long-running panel data following the same households is unavailable.
2. Deaton showed this method could track behaviour over time almost as well as real panel data, while avoiding problems such as households dropping out of a survey over the years.
3. This made the approach useful and cheaper for institutions such as the World Bank when designing large household survey programmes.

Key takeaways

• Angus Deaton won the entire Nobel Prize in Economics 2015 for his analysis of consumption, poverty, and welfare.
• He was born in Edinburgh in 1945 and was affiliated with Princeton University at the time of the award.
• With John Muellbauer, he built the Almost Ideal Demand System around 1980 to model how spending splits across goods.
• His later research showed that individual, not national, income and consumption data resolve the so-called Deaton Paradox.
• He pioneered using detailed household surveys to measure living standards and poverty in developing countries.
• He showed children need roughly 30 to 40 percent of an adult's expenditure, correcting simple per-person poverty estimates.
• His findings suggested low income causes poor nutrition, rather than poor nutrition trapping people in poverty.
• His tools remain standard for evaluating tax and policy reforms and for comparing living standards across countries.

Test yourself

Who won the Nobel Prize in Economics 2015, and where was he affiliated?

Angus Deaton won the prize; he was affiliated with Princeton University in Princeton, NJ, USA, at the time of the award.

What is a demand system?

A demand system is a set of equations showing how much of each good consumers buy, depending on all prices and their total spending.

Who did Deaton work with to build the Almost Ideal Demand System?

Deaton developed the Almost Ideal Demand System together with the economist John Muellbauer, around 1980.

What does the Deaton Paradox describe?

It describes the puzzle that aggregate consumption varied less than theory predicted, a mismatch resolved by studying individual rather than national income data.

Why did Deaton prefer household consumption data over national income data in poor countries?

Poor households often lack steady recorded wages, so consumption data from household surveys gives a more reliable measure of their living standards.

What share of adult expenditure did Deaton estimate a child typically needs?

Deaton estimated that a child typically needs roughly 30 to 40 percent of what an adult spends.

What is a pseudo panel?

A pseudo panel tracks cohorts of similar people across repeated surveys, acting as a substitute when true long-running panel data is unavailable.

When was the 2015 Economics prize announced and presented?

It was announced on 12 October 2015 and presented at the award ceremony in Stockholm on 10 December 2015.