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Illustration by Josef Gast

A slender physique and a heftier paycheck are often thought to go hand in hand, making up one more facet of workplace discrimination. But while previous studies have confirmed a positive correlation between body weight and earnings, Penn researchers, using new techniques, have found that a leg up in the job market comes not from lower adult weight but from higher birth weight.

In their as-yet unpublished report, “The Returns to Increasing Body Weight,” Dr. Jere Behrman and Dr. Mark Rosenzweig note that the benefits of increased birth weight include greater achievement in school and higher wages. According to their data, a one-pound increase in birth weight results in almost a third of a year more schooling and an increase of more than seven percent in adult earnings for a child, while a mother who smokes one pack of cigarettes per day not only lowers her baby’s birth weight but reduces the lifetime earnings of her child by over 10 percent. As Behrman, the William R. Kenan Jr. Professor of Economics, puts it: “These are substantial effects.”

The study’s findings are especially pertinent in the cases of twin and multiple births. According to Rosenzweig, the Walter H. Annenberg Professor of Social Sciences, “twins have 28 ounces less birth weight than singletons, which our estimates indicate translates into a reduction in lifetime earnings for such children of over 12 percent.” Since medical procedures that augment fertility increase the chances of multiple births, they too can impose economic costs over a child’s lifetime.

Behrman and Rosenzweig are quick to note that their study supports programs such as Medicaid that serve to increase weight at birth, while they also dispel anxieties about the long-term effects of those programs. “One might fear that policies that succeeded in increasing birth-weight have negative longer-run effects through increasing adult obesity,” Behrman posits, “but our results suggest that this is not the case.”

Such programs are not only beneficial to low-birth-weight children. “There are gains to increases in birth weights for babies who otherwise would have weighed seven or eight pounds” as well as those who weigh four or five pounds, Rosenzweig explains. And one of the gains associated with higher birth weight is increased adult height. 

“Our preferred estimates suggest that taller probably is better for white women in terms of their earnings, but that thinner or heavier does not have an impact,” Behrman says. But when asked why taller workers earn more, the researchers are hesitant to distinguish between social bias and the possibility that taller workers may be a better investment due to their higher birth weights. “If there is a social bias favoring taller workers,” notes Rosenzweig, “it may be rooted in the perception that taller workers tend to be more productive, perhaps because they had better nutrition and better development in the womb and in infancy.”

Based on questionnaires sent to pairs of twins whose records are held by the Minnesota Twins Register, the study focuses exclusively on women, which is in response to the popular belief that overweight women are most often negatively discriminated against on the basis of adult weight. However, no discrimination between lighter and heavier twins appears in the data. 

According to Behrman, earlier studies, many of which confirmed the existence of workplace discrimination based on adult weight, were not able to untangle the combined effects which adult weight, family background, and genetics have on earnings. For example, “babies with higher birth weights tend to come from families with higher incomes, with parents with higher education,” Behrman says. Such variables are so influential in determining a child’s lifetime earnings that studies which ignore them will present a skewed relationship between body weight and income. According to Rosenzweig, the use of identical twins—who have exactly the same family background and genetics—is an important step toward solving the problem of isolating the economic effects of body weight.

—Sarah Blackman C’03

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