There is a steady migration of health care workers from many low-income countries to richer ones, such as the United States and the United Kingdom. Meanwhile, in the countries they leave, people die from preventable diseases.

Michael Clemens, a fellow at the Center for Global Development research group, wondered what effect their departure had on their national medical systems. He looked at census data about health worker migration from Africa, comparing countries where many doctors and nurses have left and those where fewer have moved away.

Surprisingly, he says, it didn't seem to make a difference in commonly measured health standards. "This is from the bird's eye view, or satellite view of the continent in public health outcomes," he explains, "the chance that a typical child dies before his or her 5th birthday, mass availability of health care, the chance that any given birth is attended by skilled personnel, the chance that a child with an acute respiratory infection in the last two weeks goes to a clinic with modern facilities."

Clemens says his data show that countries that have lost many health workers still have many more at home. And those that lose workers are training new doctors and nurses. In visiting these countries to talk to health officials, the researcher discovered that in addition to out-migration, the problem is where within the country health professionals work. "There's a huge domestic drain of health professionals in all of these countries out of places and situations where these people are providing healthcare to the underserved," he reports. As an example, he points to Kenya. "The ratio of physicians per capita in urban areas to rural areas varies by a factor of almost 10 to 1. [There is a] huge movement of these people out of rural areas."

Clemens also found movement of workers from the public sector to the private sector, where care is more expensive.

Finally, Clemens says he found that in many counties, governments don't allocate enough money to pay for medical staff or facilities for them to work in. For example, in Mozambique, there are so few clinics that about half the population has never been to one. "There are all kinds of reasons for that," he points out. "Sometimes there isn't a clinic there, sometimes at the clinic you have to pay, sometimes it's not well supplied."

Clemens says the data raise important questions about allocation of resources and how that affects doctors and nurses' decisions to stay or leave. At this month's American Public Health Association annual meeting in Boston, he called for health care system reform in poor countries, to increase incentives for health workers to stay and practice in underserved areas.