Wednesday, September 21, 2011

Is smoking really the most important predictor of obesity?

Does this headline really represent the data?:

The No. 1 Reason Americans Are Getting Fatter: We're Not Smoking

The text goes on to discuss the rise of anti-smoking laws and the increase in obesity. Then at the end of the article, they discuss the actual magnitude of the effect:

"Using the traditional Blinder-Oaxaca decomposition technique" -- a social science method often used to study two groups or components with different credentials; a method, essentially, of comparing apples to oranges -- "we find that cigarette smoking has the largest effect: the decline in cigarette smoking explains about two percent of the increase in the weight measures," Baum and Chou, both professors of economics at Middle Tennessee State University and Lehigh University, respectively, explain in the paper's abstract. "The other significant factors explain less."

Two percent? Really? So non-smoking factors explain 98% of the change?

So either the model explains very little of the variation or smoking is a small contributor to the obesity epidemic, regardless of how it ranked on a list of covariates. And this doesn't even consider the possibility of correlation (obesity is rising as smoking falls) of temporal trends instead of causation.

In either case, that is not a useful headline.

No comments:

Post a Comment