To the Editor:

As the article pointed out, the researchers who did the day care study “could not randomly assign children to one kind of care or another; parents chose the kind of care that suited them.” Because there was no control group, “determining cause and effect was not possible.” Yet the word “effect” was used in reporting the outcome.

In fact, there is no good evidence of any “effect.” Parents not only chose the kind of care that suited them, they also chose the kind that suited their child. Parents are less likely to leave their child in a busy, noisy day care center if the child happens to be timid and quiet.

The underrepresentation of such children in the day care center population means that this population is biased slightly toward children with a bold, outgoing temperament. This bias alone can account for the small day care “effect” reported by the researchers.

Judith Rich Harris
Middleton, N.J., March 26, 2007
The writer is the author of two books about children’s development.