Teeth brushing correlates negatively with a child's weight

Tyler Cowen excerpts from what seems to be a very interesting book by J. Eric Oliver, titled Fat Politics: The Real Story behind America's Obesity Epidemic. Oliver's conclusion is that:

Now obviously the act of brushing one's teeth plays little direct role in a child's weight, but it is a good indicator of something else -- in what type of household the child lives. Children who brush their teeth more often are more likely to come from homes where health and hygiene are a priority...In other words, outside of genetics, the biggest factor predicting a child's weight is what type of parenting they receive.

Why yes, of course, that makes sense, its an obvious conclusion. But it got me thinking, why teeth brushing? The simple answer is: buy the book, but thats no fun. I suspect it has something to do with the variable's precision and ease of compiling. But maybe not.

For instance, it can't be any more difficult to compile data on the frequency of baths, can it? I would think bathing is an equal if not better proxy of child hygiene than teeth brushing. And, from my experience, giving baths takes significant effort on the parents behalf, more so than teeth brushing: policing water splashing, and the allocation of water toys; insuring proper soaping technique (for the older one) and the consent to soap (for the younger one), etc. It would be interesting (only to a parent, I suppose) to see if Oliver's results are robust (that is provide similar results) when a bathing proxy is used instead of or in addition to a teeth brushing proxy.

Likewise, I'd guess that a bath proxy is less noisy (more accurate) than a count of teeth brushing; that is, I suspect there is greater variation in the quality of teeth brushing across families than there is in the quality of baths. Sam and ODB I am proud to say are regular teeth brushers (twice a day, which I think is excessive, but I'd better not go there). However, to be honest, some evenings my primary objective is to get the boys in bed; I don't have the energy to force a re-brush if I suspect they did a crappy job. But what about those parents that do consistently muster the energy to force a re-brush? That effort is not captured in a count of teeth brushing. Ok, I'm buying the book.