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  • Per a new study, "one additional daycare month at age 0–2 reduces IQ by 0.5%" at ages 8 to 14, with richer kids experiencing the biggest IQ declines. Tweet This
  • If these results hold, the more money you make at work, the more likely it is that day care will damage your children. Tweet This

If you’re a working parent, struggling with the decision of who should watch your kids, I have some bad news: That choice just became a little more fraught, thanks to a new study of day care in the wealthy city of Bologna, Italy, by researchers Margherita Fort, Andrea Ichino, and Giulio Zanella.

The headline finding is that "one additional daycare month at age 0–2 reduces IQ by 0.5%" at ages 8 to 14, and there are other changes to children's personalities, as well. But the results change depending on the affluence of the child’s family, with richer kids experiencing the biggest IQ declines—while other research suggests that day care can even be good for kids who are in worse home situations. In other words, if these results hold, the more money you make at work, the more likely it is that day care will damage your children.

No one said these choices had to be easy. And no one said empirical results have to be flattering, either. Stripped of academic jargon, the findings suggest that (1) rich people hurt their kids when they use day care and (2) poorer kids are less harmed by quality day care, and sometimes even helped because the environment their families provide isn’t good enough to outshine that provided by paid child-care workers.

To study this topic, ideally one would randomly assign some parents to put their kids in day care and others not to, but this is virtually impossible to do in practice. Instead, the authors exploit some quirks of the public day care system in Bologna that have the same effect. In Bologna, parents list their day cares in order of preference, and then at over-subscribed day care centers, the slots are handed out according to an index of affluence, with the poorest parents getting access first. The cutoffs vary a lot from year-to-year, making it difficult to game the system. 

Those cutoffs serve as the source of a “natural experiment,” with the results measured through a technique called “regression discontinuity.” Parents who just barely make the cutoff for their top school put their kids in day care significantly longer than do parents who just barely miss the cutoff. (The latter either end up at a center lower on their list or get no assignment at all; there is little private day care in Bologna, so the unassigned kids are mostly cared for by family members.) Since the families very close to the line are otherwise comparable, one can use the abrupt jump in day care attendance at the cutoff to reveal the influence of day care on other variables: Is there also an abrupt change to IQ scores or personality-test results at that point?

But before digging into the results, it’s important to stress just how affluent and unrepresentative the kids subjected to the “experiment” were. Not only is Bologna a wealthy city on another continent, but the study is restricted to two-parent, both-working families—who have about twice the income as the typical Italian household. Further, while the authors have administrative data on day care attendance, the IQ and personality tests were administered in person, and only a third of the families decided to participate in the study. The average IQ of the kids was 116, substantially above 100, the overall average for the Italian population. So, while the quasi-experimental design of the study allows it to identify the effects of day care among the participating families, we have to be careful about generalizing from the findings.

As mentioned, the main result was a 0.5% decrease in IQ scores for each month that kids spent in day care because their parents just barely made the cutoff—and the result varied by parents’ socioeconomic status, as the authors show by running the analysis separately for affluence thresholds above and below the median. Above the median—meaning we’re talking about families that are well-to-do even within this wealthy group—the negative effect was 0.9% per month; below the median, the result was statistically insignificant (0.3%). The wealthier group also saw some effects on Big Five personality traits: a 1.4% decrease in “Openness” and a 1.2% decrease in “Agreeableness,” plus a borderline-significant 0.9% increase to “Neuroticism.” The effects were also stronger in girls than in boys.

The fact that the effects were small and uncertain in the bottom half of the data set should give most parents at least a little relief. Remember, in the sample as a whole, the typical income is about double that of the typical Italian household, and all the families are two-parent, dual-earners. So even the bottom half of this group is not thatbad off, and their effects might be pretty typical for the general population.

But, of course, it’s hard not to be troubled by these findings, especially if you, personally, have kids in day care so that both parents can work. (That would be me, gritting my teeth over here and frantically rifling through the study for any hint of absolution.) 

As the authors note, their results are broadly consonant with a growing body of literature. Psychologists such as Jay Belsky have argued that day care can have negative effects for decades; recent studies of Quebec’s day care expansion found bad consequences on balance but good consequences for disadvantaged families. The upshot seems to be that if your family can provide a rich, stimulating environment for your child, that environment will probably improve their lives relative to what they’d get at a commercial day care facility.

There are reasons for doubt, as always. Regular readers will know mine: If child care arrangements are so dang important, why is the “shared environment” so incredibly weak in twin and adoption studies of traits like IQ? Based on those studies, one might also wonder if effects on IQ measured at age 8 to 14 might still wear off, considering that the influence of genes on IQ increases with age, while the role of environmental factors fades out.

This is a carefully done study, though, and no working parent can finish it without developing a knot in his stomach.

Robert VerBruggen is a research fellow at the Institute for Family Studies and a deputy managing editor of National Review.