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A Comparison of the Case–Control and Case–Crossover Designs for Estimating Medical Costs of Nonfatal Fall-Related Injuries Among Older Americans

Objectives:Although the case–crossover design has been used widely in epidemiological and cost-offset studies as an alternative to the case–control design, it is rarely applied to cost-of-illness studies. In this study, costs for a series of hospitalized and nonhospitalized fall-related injuries were computed using the 2 approaches to allow for a direct comparison of the results. Research Design:We used claims data from the Medicare fee-for-service 5% Standard Analytical Files. For the case–control design, those who sustained nonfatal fall-related injuries were tracked for 1 year after their first fall, and costs were compared, using regression analysis, to annual costs for a comparison sample of nonfallers. The case–crossover design used a modified regression approach that compared monthly costs of fallers before and after fall. Results:We present unit costs for falls requiring (1) a hospitalization resulting in a live discharge, (2) an emergency department visit not resulting in an admission, and (3) falls requiring office-based or hospital outpatient visits only. Using the case–control design, these costs were $22,260, $3890, and $5040 respectively. Using the case–crossover design, these estimates were reduced to $20,920, $3230, and $4200. Conclusions:On average, estimates of the costs of fall injuries from the case–control design were between 6% and 17% greater than those from the case–crossover approach. These differences likely result from our inability to control for comorbidity differences between fallers and nonfallers in the case–control design. Under several scenarios, including unobserved heterogeneity between cases and controls, the case–crossover design, although computationally more intensive, produces more accurate results.