Cognitive Daily

Much research has found that there are IQ differences based on socioeconomic background of children: poorer children have lower IQs. But it’s possible that these differences may be due to health problems in some groups: if poor kids are more likely to get sick, wouldn’t that have some impact on their mental abilities as well?

A new study tries to control for that problem by identifying extremely healthy kids from a variety of socioeconomic backgrounds:

To find a group of healthy children, the NIH researchers screened more than 35,000 youngsters for medical, neurologic and psychiatric disorders, as well as for family histories that point to potential problems or prenatal exposure to toxins. Only 450 of the children met the strict criteria.

These children were tracked for four years while a variety of measures were taken, including IQ tests. The press release offers more details:

Income predicted IQ and academic achievement. Lower income was associated with lower IQ scores (mean IQs were 105, 110, and 115 for low-, middle- and high-income children respectively). Lower-income children were more likely to be excluded from the study because of medical or developmental conditions; the healthy low-income children who qualified performed, on average, better than previously reported population averages. “We were pleasantly surprised by how well the lower-income children did when we focused on those who were healthy,” says Waber. Although income did not predict performance on basic cognitive tasks, such as memory or reading individual words, lower-income children did score lower on tests like reading comprehension and calculation. The authors suggest that such tasks, which require more reasoning and integration of cognitive abilities, are more vulnerable to the effects of poverty-related factors than are more basic skills.

So healthy children score considerably above the mean in IQ tests, and the gap between richer and poorer kids diminishes when health is equal. This suggests that simply improving health care can do a lot to help low-income kids perform better in school. The other differences in IQ also appear to be related to factors that educators can address.

In short, these results support the notion that low IQ is largely a social and health problem, not a predetermined genetic handicap. That said, since the researchers also screened for “family histories” that could be a problem, this might indicate that genetics still play a role. I’d be interested to know what portion of children were excluded from the study for this reason.


  1. #1 Neurozone
    May 18, 2007

    I’m a little disappointed that you boil down an excellent study that will provide a very useful database of neurological and cognitive development into an easy-to-digest “nurture trumps nature” story (your last paragraph).

    Not that I want to advocate a deterministic view of cognitive development, or of “intelligence”, but the study doesn’t really address this sort of question with any rigor, because by design, a large portion of human variability – of both genetic and environmental origin – was left out of the study by only including “healthy” children.

  2. #2 Dave Munger
    May 18, 2007


    Point well taken. I shouldn’t have implied that the only take-home message of the study was “nurture trumps nature.” Clearly such a large study offers much more than that, and as you say, isn’t really designed to directly address the nature/nurture question.

  3. #3 MikeC.
    May 21, 2007

    Yes, we all know that income and IQ correlate well.

    Children from families with yearly incomes of less than $35,000 per year had a mean IQ of 105. In comparison, those with family incomes of $35,000 to $75,000 had mean IQs of 110, and those with family incomes of over $75,000 had IQs of 115.

    First of all, 105 is high even for white kids (especially in such a low income bracket). With blacks having a mean IQ of 85 and Hispanics around 90, I have to wonder how many non-white kids they even managed to grab for this study.

    To find a group of healthy children, the NIH researchers screened more than 35,000 youngsters for medical, neurologic and psychiatric disorders, as well as for family histories that point to potential problems or prenatal exposure to toxins. Only 450 of the children met the strict criteria.

    Without further details, I am suspicious anytime there is talk of screening out those with “neurological and psychiatric disorders.” How many slow kids were classed as having “learning disabilities” and excluded raising the mean IQ of the remainder?

    Also, are we talking single parent families or two parent families or a mixture of both when it comes to family incomes? Is any data on family structure available?

    I wouldn’t be surprised if there are a lot of holes in this study, but it might be interesting. Do you have access to the actual study? Can you provide more details?

  4. #4 Dave Munger
    May 21, 2007

    I wasn’t planning on going over the entire article since it’s not really a cognitive study. However you can find it online here (scroll down to the bottom of the page).

    It looks like they attempted to balance the sample to the actual racial distribution of the US. Most of the participants weren’t “rejected,” instead, their parents refused permission to participate (after all, it involved extensive MRI scanning). Only 21 percent were actually rejected because they didn’t meet the health criteria of the study.

  5. #5 acm
    May 21, 2007

    add another questioner of your final conclusion — it seems to me that there has been plenty of discussion of the role of social factors in linking wealth and IQ, be it resources available or importance placed on school work, and the more interesting notion is that mere physical health, something easily addressed by public policy, could be keeping these kids from getting further in life.

  6. #6 MikeC.
    May 21, 2007

    It appears they did a good job on the racial composition end of things. If they did another study like this though, I would like to know the IQ scores of the parents for reference.

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