Fat = lower wages on average?

Via Steven Levitt, here’s an interesting paper by Roy Wada and Erdal Tekin:  “Body Composition and Wages

This paper examines the effect of body composition on wages. We develop measures of body composition – body fat (BF) and fat-free mass (FFM) – using data on bioelectrical impedance analysis (BIA) that are available in the National Health and Nutrition Examination Survey III and estimate wage models for respondents in the National Longitudinal Survey of Youth 1979. Our results indicate that increased body fat is unambiguously associated with decreased wages for both males and females. This result is in contrast to the mixed and sometimes inconsistent results from the previous research using body mass index (BMI). We also find new evidence indicating that a higher level of fat-free body mass is consistently associated with increased hourly wages. We present further evidence that these results are not the artifacts of unobserved heterogeneity. Our findings are robust to numerous specification checks and to a large number of alternative BIA prediction equations from which the body composition measures are derived.

Our work addresses an important limitation of the current literature on the economics of obesity. Previous research relied on body weight or BMI for measuring obesity despite the growing agreement in the medical literature that they represent misleading measures of obesity because of their inability to distinguish between body fat and fat-free body mass. Body composition measures used in this paper represent significant improvements over the previously used measures because they allow for the effects of fat and fat free components of body composition to be separately identified. Our work also contributes to the growing literature on the role of non-cognitive characteristics on wage determination.

Looking very briefly through the paper, they don’t seem to be looking at what I would have thought an important factor:  relative obesity.  Wada and Tekin don’t seem to postulate a mechanism for how body fat leads to lower wages on average.  While I’m happy to accept that it may come about because of lower productivity, it also seems reasonable to ask if it’s also partially because of a selection bias by employers.  On that basis, looking at how much fat a person is carrying relative to their community average would seem to be important.

Update:  I’m obviously assuming both causality and direction of causality here, but my comment still holds.  A strong result on my suggested extra regressor would, to me, seem to provide evidence of that causality.

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