The Effect of Physical Activity on Short Run Medical Costs and Lost Work Days among US Adults
- Presenter:
Chair: Michael Hagan; Discussant: Michael Hagan Wed June 7, 2006 9:45-11:15 Room 121
Author: Eric Keuffel (ekeuffel@wharton.upenn.edu), Wharton, University of Pennsylvania.
Title: The Effect of Physical Activity on Short Run Medical Costs and Lost Work Days among US Adults
Background: Regular physical activity is frequently defined as rigorous activity sustained for at least 30 minutes three times per week. While the epidemiological implications of regular physical activity are well-established, the association between activity level and economic medical costs is not as well understood in US adults. The incentives for offering effective primary prevention programs promoting physical activity are influenced by anticipated cost savings and work days saved. Given the high rate of managed care and employee turnover in the US, short run returns are particularly important. Prior studies offer varying conclusions; some find short-run returns to physical activity others find no effect.
Objective: This study estimates the effect of regular physical activity on medical costs and days work lost after accounting for demographics, medical conditions, health insurance status and other covariates. I examine whether current year physical activity, prior year physical activity and persistent two-year physical activity result in lower medical costs and work days lost.
Data: The study data are from the 2001-2002 Medical Expenditure Panel Survey (MEPS). There are 15,269 adults (> age 16) in panel six of MEPS with data recorded in both years. MEPS records physical activity with a bivariate measure (1-rigourous physical activity at least 3 times per week/30 minutes per session; 0-not physically active) for both 2001 and 2002.
Methods: Year 2002 medical costs are modeled with a two part approach using STATA 9.1. Part I uses a probit regression to estimate the probability of positive costs. Part II estimates total medical costs conditional on positive costs with a generalized linear model (GLM gamma). Marginal effects accounting for both stages were estimated. A negative binomial model estimated the percent change in work days associated with physical activity. In each case, three separate specifications test whether current year physical activity (2002), prior year physical activity (2001) or persistent physical activity (2001 and 2002) significantly effect costs or days work missed. The base case uses robust standard errors and clusters on household.
Results: Mean 2002 medical costs in the sample are $3,025 (SD=$8,207) and 18 percent of the sample have no costs. After controlling for covariates; current, prior and persistent physical activity significantly increases (p<.10) the probability having positive costs, but only by 0.8 -1.1 percent. Physical activity is associated with lower conditional costs. Overall, point estimates for the marginal effects of current and prior year physical activity were -$32 and -$203, respectively. Mean days of work missed due to illness were 4.7 (SD=15.3 n=8,661). Persistent physical activity results in 17% fewer days missed due to sickness (p<.01).
Conclusions: Returns to physical activity in terms of medical costs are relatively modest over two years and most of the returns appear to accrue as a result of activity in the first year. Missed work days are a potentially important component when calculating the benefits of physical activity.
