COLUMBUS, Ohio -- Levels of health disparity have increased substantially for people born in the United States after 1980, according to new research.
The study also found that health disparity tends to increase as people move into middle age, before declining as people reach old age.
These two results suggest that the gap between the healthiest and least healthy people in the United States as a whole will grow larger for the next one or even two decades as the younger generations grow older and replace previous generations.
"As young people today reach middle age and preceding cohorts with a smaller health gap die off, we expect health disparities in the whole population to grow even larger," said Hui Zheng, lead author of the study and assistant professor of sociology at Ohio State University.
A lot will depend on whether future generations will continue the trend, seen in post-baby boomers, of large health disparities.
"If that trend continues, as I expect it will, health disparities in the whole population will increase in the coming decades," Zheng said.
The health gap has not always been growing, according to the study. Health disparities continuously declined from those born early in the 20th century to the baby boomer cohort, before increasing for post-baby boomer cohorts, especially those born after 1980.
Zheng conducted the study with Yang Yang of the University of North Carolina-Chapel Hill and Kenneth Land of Duke University. Their results appear in the December issue of the journal American Sociological Review.
This study provides one of the clearest, most comprehensive pictures ever of health disparities in the United States because of a methodological innovation, Zheng said.
Zheng and his colleagues combined two statistical models that allowed them, for the first time, to disentangle how health disparity over time is affected by three factors: people's age, when they were born, and the time period when their health is assessed.
"We have never before been able to look at all three of these factors together and see how each interacts with the others to affect changes in health disparities," Zheng said.
The study is based on data from the National Health Interview Survey for the 24-year period from 1984 to 2007. The survey, which includes about 30,000 people each year, is conducted by the National Center for Health Statistics.
The survey asked respondents to rate their own health on a five-point scale from poor to excellent. While this is a self-report and not based on any objective health data, previous studies have shown that self-reported health is a good indicator of objective health and is actually better at predicting mortality among the elderly than doctor assessments, Zheng said.
The researchers took into account a variety of other factors that may affect health, including gender, race, marital status, work status, education and income.
Overall, the study found that late baby boomers – those born from 1955 to 1964 – reported better health than any other generation. In addition, self-rated health has significantly declined since the late 1990s.
One of the key findings was the large gap in self-reported health that opened up for people born since 1980. That means people are more spread out among the five health categories, from excellent to poor, Zheng said.
This data can't explain why health disparities grew, but research by other sociologists provides potential explanations, Zheng said.
For one, income inequality increased dramatically in the past three decades in the United States, which could impact accessibility to health care and other important resources.
Also, an increase in immigrants, both documented and undocumented, has probably changed the distribution of health ratings in the country, while the growing obesity crisis has added to those in poor health.
Finally, a growing "digital divide" in access to medical and health information on the internet has created disparities in health knowledge among different populations, which can affect health choices and outcomes.