NATIONAL BUREAU OF ECONOMIC RESEARCH
NATIONAL BUREAU OF ECONOMIC RESEARCH

Is Poor Fitness Contagious? Evidence from Randomly Assigned Friends

Scott E. Carrell, Mark Hoekstra, James E. West

NBER Working Paper No. 16518
Issued in November 2010
NBER Program(s):   ED   HE   LS   PE

The increase in obesity over the past thirty years has led researchers to investigate the role of social networks as a contributing factor. However, several challenges make it difficult to demonstrate a causal link between friends’ physical fitness and own fitness using observational data. To overcome these problems, we exploit data from a unique setting in which individuals are randomly assigned to peer groups. We find statistically significant peer effects that are 40 to 70 percent as large as the own effect of prior fitness scores on current fitness outcomes. Evidence suggests that the effects are caused primarily by friends who were the least fit, thus supporting the provocative notion that poor physical fitness spreads on a person-to-person basis.

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Document Object Identifier (DOI): 10.3386/w16518

Published: Carrell, Scott E. & Hoekstra, Mark & West, James E., 2011. "Is poor fitness contagious?: Evidence from randomly assigned friends," Journal of Public Economics, Elsevier, vol. 95(7-8), pages 657-663, August.

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