Thursday, January 7, 2010

Women Who Don't Live Alone Add More Weight, Study Finds

New York Times article "Women Who Don't Live Alone Add More Weight, Study Finds" (January 4th, 2010) reports on two of reasons why women might put on weight after being in a relationship but two economically inspired ones.  The article reviews childbirth, more active social life, but fails to review a trivial matching market outcome.  The main result:

At the start, the women ranged in age from 18 to 23. Each woman periodically completed a survey with more than 300 questions about weight and height, age, level of education, physical activity, smoking status, alcohol consumption, medications used and a wide range of other health and health care issues.

By the end of the study, published in the January issue of The American Journal of Preventive Medicine, more than half the women had college degrees, about three-quarters had partners and half had had at least one baby. Almost all of the weight gain happened with the first baby; subsequent births had little effect.

The article does not appear to allow for the theory that in some sense, the relationship market is a market for lemons. There is some (perhaps small) fraction of the market that has a naturally heavier steady state weight. Were that subset to reveal their true type, they would obtain a worse match. After matching and growing relationship-specific capital, the women are free to gain weight, as the value of their partner's future match is less than the expected value now. The process through which Corrections imagines this happening is displayed graphically below (click to enlarge).

For a newspaper that appears to imagine market failures around every corner, the failure to bring up the idea of "sticky relationships" and incomplete information is anomalous.

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