Emily Oster, a newly minted economics PhD at the University of Chicago, has written a quick overview of her research on AIDS in Africa in Esquire. She’s asking good questions and getting answers that may mean the difference between life and death.

Yet her work seems founded on a monumentally naive notion common to economists: “Disciplines [like sociology or anthropology] believe that cultural differences — differences in how entire groups of people think and act — account for broader social and regional trends…. Economists like me don’t trust that argument. We assume everyone is fundamentally alike; we believe circumstances, not culture, drive people’s decisions, including decisions about sex and disease.

But doesn’t culture shape how we see our circumstances? Isn’t economics itself is rooted in a culture where we take for granted that people usually act in calculated, informed, individualistic, self-interested ways?

Other reporting on AIDS in Africa suggests there’s more in the world than crude utilitarian calculation. In the New York Review of Books in 2005 Helen Epstein reported that a locally developed strategy called “Zero Grazing” appeared to do much better at controlling the spread of the disease than either abstinence-only education or condom promotion. The “Zero Grazing” campaign recognized that polygamy, having several concurrent long-term sexual relationships — standard in Ugandan culture — facilitates the spread of the disease. The campaign urged men to at least avoid short-term encounters with bar girls and prostitutes. “During the Zero Grazing campaign, the proportion of Ugandan men and women with casual partners fell by 60 percent.”

The Zero Grazing campaign was abandoned — not because it didn’t work, but because it didn’t fit into either of the well-funded campaigns for abstinence and for condoms. If economics is really the study of human choices, how can it ignore different cultures when they play a part?