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You Make Pearson Cry #3: Daycare Correlates March 28, 2007

Posted by Johan in Developmental Psychology, You Make Pearson Cry.

A recent report on the NICHD study on early childcare argues that time spent in daycare is associated with disruptive behaviour:

keeping a preschooler in a day care center for a year or more increased the likelihood that the child would become disruptive in class — and that the effect persisted through the sixth grade.

The effect was slight, and well within the normal range for healthy children, the researchers found. And as expected, parents’ guidance and their genes had by far the strongest influence on how children behaved.

But the finding held up regardless of the child’s sex or family income, and regardless of the quality of the day care center. With more than two million American preschoolers attending day care, the increased disruptiveness very likely contributes to the load on teachers who must manage large classrooms, the authors argue.

On the positive side, they also found that time spent in high-quality day care centers was correlated with higher vocabulary scores through elementary school.

Controlling for genetics, parenting, family income, and gender is probably a good start, but even with such controls it’s not exactly difficult to think of other interpretations of the data:

  1. Disruptive children get put in daycare more because their parents need time off.
  2. Children in daycare have parents who generally have less time for them, in and out of daycare.
  3. Parents who put their children in daycare differ from stay-at-home parents on some other third variable

I’m also a bit curious about how they controlled for parenting, since I imagine a pretty crucial factor in parenting styles is going to be whether you believe in daycare or not. But before I spend too much time trying to make sense of the data, what does it look like, exactly?

In 2001, the authors reported that children who spent most of their day in care not provided by a parent were more likely to be disruptive in kindergarten. But this effect soon vanished for all but those children who spent a significant amount of time in day care centers.

Every year spent in such centers for at least 10 hours per week was associated with a 1 percent higher score on a standardized assessment of problem behaviors completed by teachers, said Dr. Margaret Burchinal, a co-author of the study and a psychologist at the University of North Carolina.

The statistical trick of creating extreme groups and then testing for significance tells me that they failed to find a significant correlation between time in daycare and scores on the test. By taking the extreme cases you can squeeze out a significant result, but unfortunately, you’re no longer just comparing daycare to no daycare. You’re comparing a lot of daycare to no daycare at all, and this may make your groups less comparable on other variables since you’re looking at extreme groups only, without considering the bulk of the sample that is somewhere in-between.

The effect size is a bit of a joke. a 1 percent different in scores on a test? And this is a cause for concern? Even while admitting that there were positive correlations with vocabulary scores? Making the unlikely assumption that daycare is the cause of both these effects, perhaps scoring 1 percent higher in this disruptive behaviour measure is actually a worthwhile trade-off for improved vocabulary scores?

While a large sample is always better, I think this study raises the question of how small a significant effect can be to be considered meaningful. This $200 million project (no exaggeration) could obviously afford a huge sample, to be able to get significance on a 1 percent difference. But what does this mean? Should parents take this into consideration? It’s quite possible that there is a 1 percent difference in scores on this measure for disruptive behaviour linked to a whole pile of other, less politically loaded factors that we know nothing about, because no one is looking for them.

Ultimately, a major part of why so much of basic sociology is open to interpretation is the reliance on correlational measures. Sociology, at its best, should be able to inform policy – to tell us what the best option is, for parents and for policy-makers. In this case, with a $200 million budget, I could easily see how experimental measures could be employed instead: get a sample of lower-income families and offer them free day-care in exchange for participation in the study. Out of the people who volunteer, assign half to day-care, and half as a control group. The study wouldn’t generalise beyond that part of the socioeconomic spectrum, but at least you would be able to show causation.



1. peripersonalspace - March 29, 2007

Hi Johan,
It’s one percent per year, and at least two hours a day is fairly normal for two-working parent households. Consider this; many kids will start day care at the age of 1, to be generous. During the first few years, they will spend perhaps 30-40 hours a week there, the lower amount for parents who have some flexibility. Even once they begin kindergarten, they will still spend 4-5 hrs a day in day care as most K programs are half-day (although that is changing to suit the needs of overworked parents). Once full-day school starts for the child, then the 2 hr a day amount is actually fairly normal (3 pmism to 5 pmish).
To summarize, then, the total effect is likely to be a ten percent difference in disruptivity, and the 2 hrs per day may not be as extreme as you suggest.
One other comment; high-quality day care, with low ratios of children to caregiver, age-appropriate interaction, and properly educated staff, is extremely expensive, and thus many parents are forced by economic necessity to choose lesser quality care. This is no small matter.
Your initial observations of the confounds on the placement into day care are right on!

2. Johan - March 29, 2007

Heh, it appears I posted quotes without reading them properly myself! You’re right, they’re talking about a 1 percent increase for each year, not in total as I thought. Thanks for setting me straight on that.

As I should have mentioned in the original post, I haven’t been able to locate the original study. I’m curious about how much of an increase in vocabulary they got, to compare. Not that a 10 percent increase in something bad is necessarily countered by a 10 percent increase in something good, but still…

Another issue here is what the alternative to daycare is. If one parent gives up his/her career to look after kids, what are the long-term effects on the household economy, and by extension the kid’s future?

Finally, I think you’re quite right that the quality of daycare matters too. Maybe as far as child welfare is concerned, a hypothetical low-income family is better off having a stay-at-home parent, as that parent’s income would not have covered high-quality daycare, while a higher-income family is able to pay superior daycare without spending all of one parent’s paycheck. Needless to say, the practical outcome is that while the children may be on equal footing on behavioural measures, higher-income families end up with more money to spare, while lower-income families are left with even less.

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