African-Americans who live in highly segregated counties are considerably more likely to die from lung cancer than those in counties that are less segregated, a new study has found.

The study was the first to look at segregation as a factor in lung cancer mortality. Its authors said they could not fully explain why it worsens the odds of survival for African-Americans, but hypothesized that blacks in more segregated areas may be less likely to have health insurance or access to health care and specialty doctors. It is also possible that lower levels of education mean they are less likely to seek care early, when medical treatment could make a big difference. Racial bias in the health care system might also be a factor.

“If you want to learn about someone’s health, follow him home,” said Dr. Awori J. Hayanga, a heart and lung surgeon at the University of Pittsburgh Medical Center, who was the lead author of the study.

The study, published in JAMA Surgery on Wednesday, divided all counties in the country into three levels of segregation: high, medium and low. It found that lung cancer mortality rates, a ratio of deaths to a population, were about 20 percent higher for blacks who lived in the most segregated counties, than for blacks living in the least segregated counties.