The Dartmouth Atlas has become famous for its research on regional variation in health care spending. Its work has shown up everywhere from the New Yorker to President Obama's addresses. Using the group's data, researchers published a study this week in the Archives of Internal Medicine, showing widespread variation in one of physicians' simplest acts: Prescribing antibiotics.

Researchers Yuting Zhang, Michael Steinman, and Cameron Kaplan looked at state-by-state spending on antibiotics in the Medicare Part D program. They controlled for variables such as demographics and rates of insurance. And what they found was significant variation in antibiotic use between regions - and between neighboring states.

Vermont residents spend about twice as much on antibiotics as do their neighbors in New Hampshire. There's similar variation between Texas and neighboring New Mexico.

The South tends to have the highest rate of antibiotic use, while the West comes in with the lowest.

The researchers thought about the role that disease could play in this: It would make sense, after all, if more antibiotics were prescribed to patients with greater health care needs. But that explanation didn't check out either: Rates of bacterial diseases did not correlate with antibiotic use.

"The Northeast had the highest prevalence of bacterial pneumonia, despite having the lowest use of antibiotics," the study authors note. "In contrast, the South had the highest prevalence of nonspecific acute respiratory tract infections, for which antibiotics should not necessarily be used."

The research speaks to a point that comes up again and again in the Dartmouth Atlas research: It's not always health care that drives health spending, but often the habits developed by those delivering care.