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ARTICLES:
Dimitri A. Christakis and Frederick J. Zimmerman
Violent Television Viewing During Preschool Is Associated With Antisocial Behavior During School Age
Pediatrics 2007; 120: 993-999 [Abstract] [Full text] [PDF]
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[Read P3R] Influential cases
John Sandberg   (6 November 2007)

Influential cases 6 November 2007
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John Sandberg,
Assistant Professor
McGill University

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Re: Influential cases

john.sandberg{at}mcgill.ca John Sandberg

An interesting analysis. I believe, however, on a cursory examination that there are some potentially serious problems with the main result of the paper, that boys exposed to violent TV are more likely to experience anti-social behavior problems.

My suspicion is the effect for boys is driven by one or at most 3 observations. The authors state eliminating the outlier (a boy) who watched 5 hours of 'violent' TV a day only attenuated the result for boys. What, exactly, would happen if that observation had been switched from a 1 to a 0 on the dependent variable? What would be the effect if the 3 boys with the highest TV watching were simply eliminated? It is there, after 2 hours a day that the lowess of probability rises substantively. It would be interesting to know what the BPI scores were for those three boys scoring highest on violent TV watching.

That is technical, but crucial. Still on a technical level but less obvious is why the dependent variable was coded as it was. The BPI is a continuous measure, and I am curious why this dichotomization was used. Collapsing a continuous measure into a dichotomous one loses information. It could be, for example, that boys (or girls) spending less time watching violent TV could score higher on this sub-scale for the BPI than others spending more time doing so, but when it's dichotomized they all look the same.

Given that the authors did it this way though, I am curious as to why the 88th percentile was chosen instead of the 90th, when the latter was the stated criterion. Of course, they could be the same thing, but if so, why state the 88th was chosen? If they are not the same, by choosing the lower criteria, a few extra kids are classified as having a 1 on the dependent variable than would be if the higher one was chosen.

Conflict of Interest:

None declared