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Monday, March 26, 2007

Causation vs. Correlation

In this month's issue of the Journal of Obesity is an article providing evidence that kids with a television in their room are more likely to be overweight:
Results: Overall, 22.3% (N=523) of the children were overweight, and almost half of all children (48.2%, N=1130) had a TV in their bedroom. Children with a TV in their bedroom had a higher zBMI and were significantly more likely to be overweight compared to those without a TV in their bedroom (27.3 versus 17.7%, respectively; P<0.05). After controlling for sociodemographics, physical activity, frequency of TV or movie watching and internet use, children with a TV in their bedroom who watched at least one session of TV or movies per day were more likely to be overweight compared to those without a TV in their bedroom (odds ratio=1.32, 95% confidence interval: 1.03, 1.70).
Conclusions: Having a TV in the bedroom is a risk factor for child overweight, independent of reported physical activity, participation in team sports, TV or movie watching time and internet use at home. Further study is needed to fully understand the mechanism by which having a TV in the bedroom increases children's risk for overweight.
It could be that only children who are overweight have televisions in their room or, perhaps, kids who are overweight have parents that are accommodating and therefore allow televisions in the bedroom.

The authors do avoid the solid "causation" claim by using the term "risk factor," but having a television in the bedroom seems more likely to be an additional symptom of a relatively undisciplined (from the child's point of view) living environment. It would have been nice to have a question in the survey like "Would you consider your parents strict disciplinarians?" or something like that. I wonder if that is a variable that is significantly negatively related to obesity and having a television in your bedroom.

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