Inequality effects on birth outcomes

A new addition to the inequality-undermines-health research.

Race/ethnicity and social class pattern a lot of children’s unequal outcomes, such as asthma and preterm births. That is, poor kids and those in most minority groups have worse health, on average.

Another school of thought argues that inequality itself – the spread between rich and poor – is bad for heath generally. That is, all groups suffer (some of) the negative consequences of inequality. One of the likely causes of this effect is the higher levels of stress, distrust, and violence that inequality provokes – and all the waste associated with mopping up those spills. That is the case made by Richard Wilkinson, a leader in this field, in The Impact of Inequality.

Wilkinson cites as an example a classic study of mortality rates in different U.S. metropolitan areas, represented by this figure (on p. 108 of the book):

The figure shows that death rates are lower in cities with less income inequality (moving from left to right), regardless of how rich or poor the city is overall (moving from back to front).

A new paper in the journal Pediatrics contributes to this argument. The authors, Maren E. Olson and colleagues, use data from all 50 states over 5 years to compare the average level of income, poverty rates, and amount of income inequality, with the rates of preterm births, low birthweight births, and infant mortality. Their conclusion is that states with more income inequality have higher rates of adverse birth outcomes, even at the same levels of average income.

In this figure, for example, they array states according to their level of income inequality (the Gini index, which is 0 at perfect equality and 1 at perfect inequality), showing their rates of very low birth weights.

Some of the inequality effects they find are because there are more very poor people in places with more inequality, and unhealthy birth outcomes are more common among the poor. However, the statistical models show (some) inequality effects even holding constant poverty levels.

In the U.S., high income inequality is usually found in places with a higher proportion of African Americans. Notice the cluster of high-inequality, poor-health states in the top right of the figure — all Southern states. That complicates a study like this, because when two things go together you can’t tell which is more important.* This is not just a statistical problem, because if White racism is more intense in places with more Blacks (which we have lots of evidence for), then it might be racism, rather than income inequality, that produces effects like this.

I like the authors’ response to this issue:

…the association between income inequality and infants’ health is relevant regardless of the racial composition of the population. … Although race is worth noting in any study of the associations between income inequality and health, it is not a population-level variable that could or should be altered through public health or policy interventions. On the basis of the results of this study, part of the solution to the very real problem of health disparities experienced by minority populations is to decrease the degree of absolute and relative poverty they experience.

We could add the level of racism as one factor that “could or should be altered,” but these are not mutually exclusive problems.

* Think of this question: what causes depression, living in the dark at high latitudes or living in cold places?

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