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There are several ways to ways to tally up obesity’s costs, each with their pros and cons. Learn more about prevalence-based and incidence-based methods for estimating obesity’s cost.

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A Closer Look at Calculating Obesity’s Economic Toll

Although cost-of-illness analyses are common for many diseases, such analyses have proven challenging for obesity. (1) Treatment for obesity itself with either medical or surgical therapies is rare, thus the costs associated with obesity are largely those that come from treating diseases linked to obesity, such as diabetes and cardiovascular disease. The constantly expanding list of medical conditions associated with obesity has made it difficult to accurately estimate the cost of obesity. (2) Methodological issues also complicate estimation of obesity-related costs. This article briefly describes the strengths and limitations of prevalence- and incidence-based methods for estimating obesity’s cost.

Prevalence-Based Cost Estimate Methods

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In one of the earliest analyses of the economic burden of obesity, Colditz used a prevalence-based (cross-sectional) methodology to estimate the direct and indirect costs of obesity. (3) For direct costs, he identified the prevalence of diseases incurred by obese individuals, the proportion of these diseases attributable to obesity (population attributable risk, or PAR), and their associated costs (direct costs attributable to obesity = PAR x average medical expenditure among all cases). For indirect costs, he estimated the present value of future earnings lost by individuals who died prematurely. According to this analysis, the cost of obesity in the United States in 1986 was $39 billion, or 5.5 percent of total healthcare spending. (3)

The strengths of prevalence-based methods are that data are readily available, and the results offer a snapshot in time of obesity’s annual costs. (4)

The chief limitation of a prevalence-based approach is that it may underestimate or overestimate the true cost of obesity. The recognition of new obesity-related diseases implies that a prevalence-based approach would offer a lower-limit estimate. (4) At the same time, though, prevalence-based estimates may overestimate the cost of obesity since conditions often overlap, and thus there is the possibility of double-counting expenditures. For example, an obese individual may make one doctor visit for management of both high blood pressure and diabetes and incur just one outpatient medical cost, rather than two costs for two visits. (4)

Another limitation of prevalence-based analyses is their assumption that the share of costs attributable to obesity equals the share of disease prevalence—an assumption that may not be true. (5) For instance, 20 percent of all cases of hypertension may be due obesity, but obesity-related hypertension may account for more than 20 percent of the total cost of treating hypertension.

Prevalence-based analyses are also limited by the precision of the PAR, which is based on epidemiologic estimates of the relation between obesity and a disease. If researchers use poor-quality data to estimate a PAR, or use data that has not adequately controlled for other factors that can affect disease risk, the accuracy of the PAR, and in turn the cost estimate, will suffer. (5)

Incidence-Based Cost Estimate Methods

Incidence-based approaches offer an alternative to prevalence-based approaches. An incidence-based approach follows individuals in a study population, records their healthcare expenses over time, and compares the expenses of obese individuals with those of their normal-weight counterparts.

One advantage of this approach over the prevalence-based approach is that it allows for greater statistical adjustment for obesity-related and competing causes of healthcare expenditures. (1) Unfortunately, such studies are data intensive, meaning few have been done. (4) A recent systematic review identified only five individual-level studies in the U.S. that followed people over time (that is, were longitudinal), and that used the incidence-based approach to examine the economic burden of obesity. (1)

One limitation of the incidence-based approach is that studies can rarely follow subjects long enough to determine lifetime costs of obesity. That’s why some investigators have used simulation methods to project future disease incidence and costs as a function of current disease risk profiles. (4) Most of the incidence-based studies to date have not modeled future weight gain but instead have held weight constant from baseline. Given that weight gain throughout adulthood can be substantial, these estimates are conservative. (4)

References

1. Withrow D, Alter DA. The economic burden of obesity worldwide: a systematic review of the direct costs of obesity. Obes Rev. 2010. DOI: 10.1111/j.1467-789X.2009.00712.x.

2. Finkelstein EA, Trogdon JG, Cohen JW, Dietz W. Annual medical spending attributable to obesity: payer- and service-specific estimates. Health Aff (Millwood). 2009; 28:w822–31.

3. Colditz GA. Economic costs of obesity. Am J Clin Nutr. 1992; 55:503S–507S.

4. Colditz GW, Wang, YC. Economic costs of obesity. In: Hu F, Obesity Epidemiology. New York: Oxford University Press, Inc., 2008.

5. Trogdon JG, Finkelstein EA, Hylands T, Dellea PS, Kamal-Bahl SJ. Indirect costs of obesity: a review of the current literature. Obes Rev. 2008; 9:489–500.

1. Withrow D, Alter DA. The economic burden of obesity worldwide: a systematic review of the direct costs of obesity. Obes Rev. 2010. DOI: 10.1111/j.1467-789X.2009.00712.x.

2. Finkelstein EA, Trogdon JG, Cohen JW, Dietz W. Annual medical spending attributable to obesity: payer- and service-specific estimates. Health Aff (Millwood). 2009; 28:w822–31.

3. Colditz GA. Economic costs of obesity. Am J Clin Nutr. 1992; 55:503S–507S.

4. Colditz GW, Wang, YC. Economic costs of obesity. In: Hu F, Obesity Epidemiology. New York: Oxford University Press, Inc., 2008.

5. Trogdon JG, Finkelstein EA, Hylands T, Dellea PS, Kamal-Bahl SJ. Indirect costs of obesity: a review of the current literature. Obes Rev. 2008; 9:489–500.

6. Cawley J, Meyerhoefer C. The medical care costs of obesity: an instrumental variables approach. Working paper 16467. Cambridge, MA, USA: National Bureau of Economic Research, 2010.

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