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Sunday, 17 October 2004

This presentation is part of: Poster Session - Public Health; Methodological Advances

A COMPARISON OF THE CASE-CONTROL AND CASE-CROSSOVER DESIGNS FOR ESTIMATING COSTS OF FALL-RELATED INJURIES AMONG MEDICARE BENEFICIARIES 65 AND OLDER

PURPOSE: Although the case-crossover design has been used widely in epidemiological studies as an alternative to the case-control design, it is rarely applied to cost-of-illness studies. In this study, unit costs for a series of hospitalized and non-hospitalized injuries are computed using the two approaches to allow for a direct comparison of the results.

METHODS: We use claims data from the Medicare fee-for-service 5% Standard Analytical Files. The claims contain detailed payment information for all covered services for hospital inpatient, hospital outpatient, skilled nursing, home health, hospice, physicians/supplier services and durable medical equipment. For the case-control design, fallers are tracked for 1-year after their first fall, and costs are compared to annual costs for a comparison sample of non-fallers. A generalized linear regression model with a logged dependent variable and a gamma distribution is used to estimate costs while controlling for covariates (including differences in demographics and comorbidities between fallers and non-fallers). The case-crossover sample compares monthly costs of fallers pre- and post-fall and is again estimated using a generalized linear regression model with a logged dependent variable and gamma distribution. This model also uses a cluster option to account for clustering within individuals across months.

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 are $22,260; $3,890; and $5,040 respectively. Using the case-crossover design, these estimates are reduced to $20,920; $3,230; and $4,200.

CONCLUSION: Estimates from the case-control design are between 6% and 20% greater than those from the case-crossover approach. These differences likely result from our inability to control for comorbidity differences between fallers and non-fallers in the case-control design. The case-crossover design, although computationally more intensive, avoids this pitfall and allows for producing more accurate estimates.

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See more of The 26th Annual Meeting of the Society for Medical Decision Making (October 17-20, 2004)