A comparison of the case-control and case-crossover designs for estimating medical costs of nonfatal fall-related injuries among older Americans.
OBJECTIVE
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.


METHODS
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.
Finkelstein
Eric A
EA
RTI International, Research Triangle Park, NC 27709, USA. finkelse@rti.org
Chen
Hong
H
Miller
Ted R
TR
Corso
Phaedra S
PS
Stevens
Judy A
JA
D000058:Accidental Falls / Q000191:economics*; D000368:Aged; D000553:Ambulatory Care / Q000191:economics; D016022:Case-Control Studies; D018592:Cross-Over Studies; D004636:Emergency Service, Hospital / Q000191:economics; D018588:Fee-for-Service Plans; D005260:Female; D005102:Health Expenditures; D006760:Hospitalization / Q000191:economics; D006801:Humans; D008297:Male; D006278:Medicare; D012044:Regression Analysis; D014481:United States; D014947:Wounds and Injuries / Q000191:economics*