A new study provides the best evidence to date that higher levelsof income inequality in the United States actually lead to moredeaths in the country over a period of years. The findings suggest that income inequality at any one pointdoesn't work instantaneously - it begins increasing mortality rates5 years later, and its influence peaks after 7 years, before fadingafter 12 years. "This finding is striking and it supports the argument that incomeinequality is a public health concern," said Hui Zheng, author ofthe study and assistant professor of sociology at Ohio StateUniversity. The study appears online in the journal Social Science and Medicine and will be published in a future print edition. Many other studies have examined the impact of income inequality onmortality and have come up with mixed results, according to Zheng.But he thinks that this study overcomes problems in previousresearch by using a different data structure and statistical model(called a discrete-time hazard model). |
Zheng used data from the U.S. National Health Interview Survey from1986 to 2004 with mortality follow-up data from 1986-2006. Hisfinal sample included more than 700,000 people aged 30 and up. The study measured income inequality using three different methods,including the most commonly used metric - the Gini coefficient,calculated by the U.S. Census Bureau.
All three methods resulted insimilar findings. The Gini coefficient ranges in value from 0 (indicating completeequality, with everyone earning the same income) to 1 (completeinequality, with one person earning all income). The Gini coefficient has been steadily rising in the United Statesin recent decades, from .403 in 1980 to .469 in 2010. In this study, Zheng found that a 0.01 rise in the Gini coefficientincreases the cumulative odds of death by 122 percent in thefollowing 12 years.
This is after taking into account a widevariety of factors that may also influence mortality, including aperson's age, gender, race, marital status, education, work statusand family income. "Income inequality has a substantial effect on mortality," he said. But if income inequality does indeed affect mortality rates, whyhave other studies found mixed results? Zheng reviewed 79 previousstudies to look for the reasons. The 11 best studies looked atincome inequality at a particular point in time to see how itaffected mortality rates at a specified time later.
"But current mortality isn't just affected by income inequality atone time, say 10 years ago. It is also affected by incomeinequality 9 years ago, and 11 years ago, and the current level ofinequality, and so on," he said. In this study, Zheng was able to look at deaths in a particularyear and control for income inequality for each of up to 21 yearspreceding the death. "For the first time, we can clearly capture the long-term effect ofincome inequality on health," he said.
"Previous studies are likelyto miss the effect if the mortality follow-up period is too shortfor income inequality to exert its impact or too long for incomeinequality to maintain its influence." Other scholars have hypothesized why income inequality may lead tohigher death rates. One reason may be that, in countries withrising income inequality, the interests of the wealthy tend todiverge from the rest of society. The wealthiest people may pushgovernment for more services for themselves, rather than invest inpublic goods like education or affordable medical services -services that can affect health for the majority of people. In addition, inequality reduces social cohesion and trust, whichstudies suggest is important to individual health. Finally, inequality may create a culture of upward comparison,where many people see the lifestyles of the rich and feel theycan't live up to expectations.
That can lead to negative views ofthemselves, frustration and depression , which have been linked to sickness and mortality. "None of these negative factors caused by income inequality willhave an immediate effect on chronic illness and mortality," Zhengsaid. "But over time they take a toll on health, which can eventuallylead to sickness and death. That's why this study found that ittakes 5 years for the effects of income inequality to appear." These results also support findings from a 2009 study by Zheng thatexamined how income inequality affected Americans' self-ratedhealth. That study found that the dramatic increase in incomeinequality from 1972 to 2004 increased the odds of worse self-ratedhealth by 9.4 percent.
That study only looked at the instantaneousimpact on self-rated health. The impact should be even larger if ithad taken into account the long term impact, he said. "The evidence is growing clearer that income inequality has along-term detrimental impact on individual health and mortality,"he said. Additional References Citations.
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