Public transit, obesity, and medical costs: assessing the magnitudes.

TL;DR: While no silver bullet, walking associated with public transit can have a substantial impact on obesity, costs, and well-being.

About: This article is published in Preventive Medicine.The article was published on 2008-01-01 and is currently open access. It has received 127 citations till now. The article focuses on the topics: Population & Present value of costs.

Summary

Introduction

• A topic of much recent interest is the degree to which public transportation may increase exercise through walking.
• Because residents typically select their communities, much remains unclear about the causal influence of environment on activity (Handy and Mokhtarian, 2005; Ogilvie et al., 2006).
• The amount of additional physical activity associated with public transportation appears potentially significant.

Methods

• Estimating additional walking associated with public transit Part of the 2001 NHTS included a daily travel diary in which household respondents were asked to self-report all trips, their purposes, starting and ending times, and the means of transportation during an assigned travel day.
• I can only compare my estimates to those of Wener and Evans (2007), who collect objective measures of extra walking using pedometers.
• I interpret β as the additional walking associated with transit use.
• Of the 105,942 individuals in the adult subsample, 39,782 filled out the entire survey and have a sample weight, and 28,771 records contain all covariates.

Forecasting obesity prevalence

• These statistics are reported by Flegal et al. (2002) and Ogden et al. (2006), who examine data from the 1960–1962 National Health Examination Survey (NHES) and subsequent NHANES waves.
• “College degree” includes the bachelor but not the associate.
• It is convenient to combine the estimates of Sturm, who examines additional costs under age 65, with those of Lakdawalla et al., who explore costs over 70.
• In each year of the projection, I apply the forecast obesity prevalence rate to the additional per capita spending associated with obesity.
• In addition to increased medical costs, obesity also threatens the quality of health and well-being, most notably later in life, and I measure these costs as well.

Results

• Additional walking through transit Table 1 describes the characteristics of the weighted NHTS sample of adults, where the observations are person-days.
• An almost equally large share, 1.9%, reported walking as their sole means of transit on their travel day, but these were primarily recreational walkers rather than commuters.
• Column 1 reports ordinary least squares estimates, while columns 2–6 re marginal effects of each Tobit are the partial derivatives of the expected value o significance, with ⁎⁎⁎ at the 1% level, ⁎⁎ at 5%, and ⁎ at the 10% level.
• No el of daily walking time as shown in Eq. (1) in the text, with standard errors in port Tobit estimates under various alternative specifications, where the reported f the observed walking time variable.

Reductions in obesity

• The distribution of excess energy stored reported by Hill et al. (2003) reveals that these levels of additional expenditure could eliminate weight gain in approximately 43%, 50%, or 60% of the population.
• The assumed QALY weight of a life-year spent disabled is 0.8.

Obesity prevalence scenarios

• An OLS regression line through the historical obesity prevalence data in Fig. 1 has a slope equal to roughly 0.5% per year, significant at the 1% level.
• These three scenarios are depicted in the right-hand side of Fig. 1 beneath the baseline projection.
• Present value per person depending on the intensity, and about 80% of the savings is public money.

Discussion

• The objective of this paper was to explore the potential benefits of shifting an average U.S. citizen from driving to using public transit.
• Results hinge on an unknown that is difficult to estimate with great confidence: the additional physical activity associated with public transit.
• It seems unlikely that anyone rationally chooses to be obese (Cutler et al., 2003), so anti-obesity policies in general are unlikely to trigger rational behavior that directly counteracts the intent, as might be an issue with anti-smoking policies if addiction is rational.
• It could be that public transit indeed causes more physical activity, but individuals offset the potential health effects by eating more.
• I have chosen a simple linear extrapolation of the historical trend, which has been a 0.5% linear rate of increase since the inception of the NHES/NHANES survey in 1960.

Conclusion

• Use of public transit is associated with more walking, by about 8.3 extra minutes per day.
• This is not enough walking to halt the spread of obesity, but it could substantially reduce it.
• The present value of medical expenditure savings per person could be $5500, while the value of reduced disability could be even greater.

Figures

Table 1 Sample characteristics of adults in the 2001 National Household Travel Survey

Fig. 1. Adult obesity rates in the United States, historical and projected. Data are the rate of obesity, defined as body mass index (BMI) 30 or greater, for the adult population measured in the National Health Examination Survey (NHES) and National Health and Nutrition Examination Survey (NHANES). Obesity rates are calculated by Flegal et al. (2002) and Ogden et al. (2006), appear as circles in the figure, and are plotted at the midpoint of the NHANES examination period. The dashed line represents a simple forward extrapolation from the most recent data point of the average annual increase in the rate, 0.5%, which is estimated by ordinary least squares regression of all historical data on time.

Table 4 The effect of additional walking due to public transit on health status and its value

Table 3 The effect of additional walking on the present value of additional health care spending associated with obesity, 2007 dollars

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Public transit, obesity, and medical costs: assessing the magnitudes" ?

This paper assesses the potential benefits of increased walking and reduced obesity associated with taking public transit in terms of dollars of medical costs saved and disability avoided. Further research is warranted on the net impact of transit usage on all behaviors, including caloric intake and other types of exercise, and on whether policies can promote transit usage at acceptable cost.