This evidence supports on-the-ground observation in the United States. Kathryn Edin and Luke Shaefer have documented the daily horrors of life for the several million people in the United States who actually do live on $2 a day, in both urban and rural America. Matthew Desmond’s ethnography of Milwaukee explores the nightmare of finding urban shelter among the American poor.

It is hard to imagine poverty that is worse than this, anywhere in the world. Indeed, it is precisely the cost and difficulty of housing that makes for so much misery for so many Americans, and it is precisely these costs that are missed in the World Bank’s global counts.

Of course, people live longer and have healthier lives in rich countries. With only a few (and usually scandalous) exceptions, water is safe to drink, food is safe to eat, sanitation is universal, and some sort of medical care is available to everyone. Yet all these essentials of health are more likely to be lacking for poorer Americans. Even for the whole population, life expectancy in the United States is lower than we would expect given its national income, and there are places — the Mississippi Delta and much of Appalachia — where life expectancy is lower than in Bangladesh and Vietnam.

Beyond that, many Americans, especially whites with no more than a high school education, have seen worsening health: As my research with my wife, the Princeton economist Anne Case, has demonstrated, for this group life expectancy is falling; mortality rates from drugs, alcohol and suicide are rising; and the long historical decline in mortality from heart disease has come to a halt.

I believe, as do most people, that we have an obligation to assist the truly destitute. For those who believe that aid is effective, this is reflected in their own giving, or by supporting national and international organizations like the United States Agency for International Development, the World Bank or Oxfam.

For years, in determining this spending, the needs of poor Americans (or poor Europeans) have received little priority relative to the needs of Africans or Asians. As an economist concerned with global poverty, I have long accepted this practical and ethical framework. In my own giving, I have prioritized the faraway poor over the poor at home.