The study, whose lead author is CDC epidemiologist Judith Weissman, does not address the issue of causality—in other words, whether mental health problems lead to more economic hardship or whether economic hardship leads to more mental health problems. But most researchers believe the process works in both directions. Studies have shown, for example, that infants and toddlers growing up in low-income communities are more likely to experience the kind of “toxic stress” (neglect, abuse, seeing violence in the home) that can hinder brain development and lead to mental illness in adulthood. Additional studies have suggested, though not conclusively, that adults who become unemployed are more likely to develop depression.

A new study from the Centers for Disease Control— Serious Psychological Distress Among Adults: United States, 2009–2013 —confirms what common sense and the experts have long told us: The poor have more mental health problems than the rich. The study was derived from responses over five years in the in-person National Health Interview Survey. Jonathan Cohn reports At any rate, it's no surprise that people with mental health issues are more likely to have a tough time finding a good job or keeping one. And that means they are less likely to have health insurance that enables them to get treatment. The availability of mental health coverage through the Affordable Care Act should make some difference in this regard. But the CDC data are mostly too early to show whether there has already been change on that front. A study published last August indicated that a 2010 ACA provision allowing children aged 18-25 to get mental health coverage on their parents' insurance plans had boosted by 5.3 percent the proportion of this cohort that sought treatment for mental illness or disorders.

But, as Cohn points out, getting insurance doesn't solve all the problems for low-income people because many providers won't accept it and the out-of-pocket costs are often very high. The National Alliance on Mental Illiness is pushing for various fixes, including requiring insurers to post accurate directories of treatment providers that are accepting new patients, requiring them to publish standards they use to approve or deny mental health claims, requiring the federal Department of Health and Human Services to mandate that all health plans "provide clear, understandable, easy to access information about health benefits," and urging Congress and the executive branch to find ways to cut out-of-pocket costs for low-income Americans.

That ought to be an agenda item for activists who pledged years ago to improve an ACA that they feel falls short. As long as millions of Americans have no health insurance—for mental health matters as well as others—those pledges will remain unfulfilled.