It has been a common belief that, while income inequality has risen rapidly in the west generally, and the United States specifically, inequality of consumption has travelled a much milder trajectory. Many reasons have been given for this effect, which was seen in a number of studies and generally assumed to be true.
Some argued that the divergence between the two was due to the unsustainable bubble of consumer credit; while the rich were getting richer faster than the poor were getting less poor, both ended up with mobile phones and flatscreen TVs, but the latter bought them with borrowed money. This, of course, leads those like Edwina Currie to argue that poor people aren't really poor because they have nice things.
Another interesting point raised off the back of the figures was the claim that it was entirely understandable, since the marginal utility of money declines pretty quickly. Thus, the explanation goes, income growth at the top end doesn't increase consumption all that much, since there isn't much to spend that money on. If this is true, then consumption inequality would indeed rise slower than income inequality in countries where absolute poverty is rare.
Now, though, it seems that both these arguments may come from faulty premises. A new paper from the American National Bureau of Economic Research argues that actually, consumption inequality has been rising at much the same rate as income inequality.
The authors write (£):
There is now mounting evidence that the [consumer expenditure survey, the source of many of the claims of divergence] is plagued by serious non-classical measurement error, which hinders the extent to which definitive conclusions can be made about the extent to which consumption inequality has evolved over the last three decades. . .
Consumption inequality within the U.S. between 1980 and 2010 has increased by nearly the same amount as income inequality
Across every other measure of consumption we analyzed, consumption inequality increased substantially.
Of course, the same questions apply to consumption inequality as do to income inequality: why does it actually matter? So long as everyone can consume the essentials, does the difference between them and the rich have any effect?
The answer is one that Adam Smith hit upon over two centuries ago (although you are unlikely to find the libertarian Adam Smith Institute quoting it): what the rich can afford has a material effect on what is essential.
In The Wealth of Nations, published 1776, Smith wrote:
A linen shirt, for example, is, strictly speaking, not a necessary of life. The Greeks and Romans lived, I suppose, very comfortably, though they had no linen. But in the present times, through the greater part of Europe, a creditable day-labourer would be ashamed to appear in public without a linen shirt, the want of which would be supposed to denote that disgraceful degree of poverty, which, it is presumed, nobody can well fall into without extreme bad conduct.
Custom, in the same manner, has rendered leather shoes a necessary of life in England. The poorest creditable person, of either sex, would be ashamed to appear in public without them. In Scotland, custom has rendered them a necessary of life to the lowest order of men; but not to the same order of women, who may, without any discredit, walk about barefooted.
In France, they are necessaries neither to men nor to women; the lowest rank of both sexes appearing there publicly, without any discredit, sometimes in wooden shoes, and sometimes barefooted. Under necessaries, therefore, I comprehend, not only those things which nature, but those things which the established rules of decency have rendered necessary to the lowest rank of people.
Cartoonist Ruben Bolling sums the argument up in eight panels.
To Smith's list we can reasonably add mobile phones (required for much shift work), computers (essential for jobseeking) and, in much of the country, cars. Consumption inequality adds to this list from the top end even as the bottom end remains unable to afford it.
Hat tip to Matt Yglesias for the paper.