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820 23 MAY 2014 • VOL 344 ISSUE 6186 sciencemag.org SCIENCE

SPECIAL SECTION THE SCIENCE OF INEQUALIT Y

developing methods of analysis, extracting causal inferences, formulating hypotheses

—all of this is the stuff of science and is

more possible with economic data than

ever before. Even physicists have jumped

into the game, arguing that physical laws

may help explain why inequality seems so

intractable (see p. 828).

In the United States, the new informa-

tion suggests a wide rift between top and

bottom. Tax data from the WTID suggest

that today the top 1% control nearly 20%

of U.S. income, up from about 8% in the

1970s. But inequality is increasing within

the 99%, too, as a consequence of a grow-

ing premium on college and postgradu-

ate education: The fates of the tech-savvy

worker at Google and the blue-collar em-

ployee at General Motors have been de-

coupled (see Autor, p. 843). According to

surveys by the Census Bureau, in 2012 the

richest 20% of Americans enjoyed more

than 50% of the nation’s total income, up

from 43% in 1967. The middle 20%—the

actual middle class—received only about

14% of all income, and the poorest got a

mere 3% (see graphic).

Flip to a world map, and America’s in-

equality, despite reaching levels last seen

in the Gilded Age, turns out to be far from

extreme. Many nations, especially emerg-

ing economies, have even larger chasms

between the super-rich and the poor. One

widely used metric, the Gini coefficient,

estimates inequality as an index between

0—at which point everyone has exactly

equal incomes—to 1, in which a single per-

son takes all the income and the rest get

nothing. The U.S. Gini, at 0.40 in 2010,

seems relatively high compared with, for

example, Japan at 0.32. But South Africa is

a sky-high 0.7.

Many assume that governments in

emerging economies have chosen to favor

growth even at the cost of inequality on the

The world Gini data, collected between 2008 and

2012, cover 117 countries and were prepared for

Science by researchers Branko Milanovic and Janet

Gornick of the Luxembourg Income Study Center at

the City University of New York’s Graduate Center.

U.S. data are based on 2012 U.S. Census Bureau

surveys of 122,459 households.

A world of difference Countries vary widely in inequality

Compiled by Emily Underwood

50%

40%

30%

20%

10%

Lowest

ffth

A sharp divide Shares of U.S. income by quintile, 2012

Second ffth

Third ffth

Fourth ffth

Highest ffth

14.4

3.2

Source: U.S. Census Bureau

8.38.3

Source: Piketty and Saez, 2013

Winners take all

Top 1% income share in the United States

25%

20%

15%

10%

1913 1930 1945 1960 1978 1995 2011

Excluding capital gains

Including capital gains

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23 MAY 2014 • VOL 344 ISSUE 6186 821SCIENCE sciencemag.org

grounds that “a rising tide lifts all boats.”

But evidence that this trade-off is necessary

is sparse, and recent data show that poli-

cies to reduce inequality need not stymie

growth (see Ravallion, p. 851).

What of those at the bottom? Research

has established a base of knowledge about

the harmful effects of disadvantageous

circumstances on education and health.

These influences can begin early in life,

even prenatally (see Aizer and Currie, p.

856). But researchers are still exploring

whether the stress of being low-ranked it-

self adds to the poor’s burden, causing ill-

ness and even early death (see p. 829). In

addition, psychological mechanisms may

spur a negative feedback loop in which

poor individuals behave in ways that help

keep them poor (see Haushofer and Fehr,

p. 862).

Harsh as life can be for those at the bot-

tom, the opportunity to move up the ladder

can compensate. Newly available data from

taxes and other records promise to yield

insights into intergenerational mobility, in

which children advance from their parents’

socioeconomic status. But so far, researchers

have a relatively limited view of how and why

people move into different social, as well as

economic, classes (see p. 836 and http://scim.

ag/sci_inequality; also see Corak, p. 812).

Few would deny that excessive inequal-

ity can be unhealthy for societies and

economies, but the new data don’t pin-

point a desirable level. They do show that

the forces that foster inequality—from the

patchy distribution of resources among an-

cient hunter-gatherers to the sheer earning

power of capital today—are many and po-

tent. It is up to society to decide whether,

and how, to restrain them (see p. 783).

Gilbert Chin is a senior editor for Science

and Elizabeth Culotta is a deputy news

editor for Science.

No data

0.455–0.499

0.5–0.544

0.545–0.599

0.6–0.644

0.655–0.699

0.23–0.274

0.275–0.319

0.32–0.364

0.365–0.409

0.41–0.454

Quantifying inequality Economists use a metric called the Gini coefcient

to estimate inequality on a scale from perfectly

equal (0) to perfectly unequal (1).

More equal

Less equal

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A world of difference Emily Underwood

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