"We know low-socioeconomic-status families are under a lot of stress — all kinds of stress. When you are poor, when it rains it pours. You may have housing problems. You may have more conflict in the family. There's a lot more pressure in paying the bills. You'll probably end up moving more often. There's a lot more demands on low-income families. We know that produces stress in families, including on the children," Evans said.
For the new study, Evans and a colleague rated the level of stress each child experienced using a scale known as "allostatic load." The score was based on the results of tests the children were given when they were ages 9 and 13 to measure their levels of the stress hormones cortisol, epinephrine and norepinephrine, as well as their blood pressure and body mass index....The subjects also underwent tests at age 17 to measure their working memory, which is the ability to remember information in the short term. Working memory is crucial for everyday activities as well as for forming long-term memories.
"It's critical for learning," Evans said. "If you don't have good working memory, you can't do things like hold a phone number in your head or develop a vocabulary."
When the researchers analyzed the relationships among how long the children lived in poverty, their allostatic load and their later working memory, they found a clear relationship: The longer they lived in poverty, the higher their allostatic load and the lower they tended to score on working-memory tests. Those who spent their entire childhood in poverty scored about 20 percent lower on working memory than those who were never poor, Evans said.
This is, in a sense, discouraging news. You can't solve problems unless you first understand the objective reality underlying them, so if Evans's results are confirmed it will be good in that sense. But stress? What would it take to make the lives of poor children substantially less stressful? The resources to tackle that could be harder to marshal than the resources to eradicate poverty itself. If stress really turns out to be a significant factor in the cognitive development of poor children, addressing the problem may have just gotten harder, not easier.