Eliminating health disparities between races is a goal of many groups and organizations, but a team of sociologists suggests that finding the reasons for the differences in the timing of black and white deaths may be trickier than once thought.

Life expectancies for black people are shorter and more uncertain, on average, than to those of whites, according to Glenn Firebaugh, Roy C. Buck Professor of American Institutions and professor of sociology and demography, Penn State. A higher lifespan variability -- the variability in the ages at which people die -- among blacks is usually explained by higher rates of certain causes of death, such as murder, which are more common among the young. However, the researchers found that higher rates of other causes of white deaths among the young appear to offset this.

"We initially suspected that the greater variance in lifespan for blacks would be a result of differences in the causes of death, for instance, the higher homicide rates among blacks," said Glenn Firebaugh. "But, as we looked closer, we saw that suicides and deaths due to drug poisoning -- deaths that are more common among whites -- offset the higher homicide rates for blacks."

Black homicide rates account for about 38 percent of the greater variance for blacks. However, the higher rates of white suicide and death due to drug overdose nearly cancels out the homicide effect, Firebaugh said.

Taken all together, differences in causes of death account for only about 13 percent of the difference in lifespan variability between blacks and whites, according to the researchers, who report their findings in the current issue of Demography.

"If you could magically change everything and make it so blacks and whites died of exactly the same causes, that would have surprisingly little effect on the difference in lifespan variability," said Firebaugh. "About 87 percent of the overall difference would persist."

In addition to behavioral reasons for lifespan uncertainty, researchers have also theorized that differences in medical treatment of and health prevention strategies for black and white patients may explain some of the difference in the variability of lifespan.

The researchers suggest that interventions to reduce this disparity may be more effective if they target sex, as well as race.

"With regard to policy, our results indicate the importance of sex-specific intervention to reduce racial disparities," the researchers said. "In the case of HIV/AIDS, for example, there is greater potential for significant reduction of the racial gap when men are targeted. The opposite is true for heart disease and diabetes, where interventions focused on women are more likely to narrow the gap."

Focusing on preventing specific causes of death, such as homicide and HIV/AIDS deaths, would help significantly cut the disparity. Eliminating the difference in deaths due to those two causes would cut the black-white disparity in lifespan variance by half, the researchers said.

Lifespan uncertainty is important because it may have a ripple effect for people and society, according to Firebaugh, who worked with Francesco Acciai, Aggie Noah, Christopher Prather, all graduate students in sociology and demography, Penn State and Claudia Nau, postdoctoral fellow in public health, the Johns Hopkins Global Centre for Childhood Obesity.

"This isn't part of the study, of course, but the uncertainty in lifespan could lead to uncertainty about the future," said Firebaugh. "One could imagine, for instance, that a consequence of people facing more uncertain lifespans would be that they change the way they plan, or don't plan, for health or education, for example, or for investing in retirement."