Objective: The purpose of this study was to measure geographic variations in the availability and use of chiropractic under Medicare.
Methods: A cross-sectional design was used to analyze a large nationally representative sample of Medicare data. Data from a 20% representative sample of all paid Medicare Part B fee-for-service claims for 2007 were merged with files containing beneficiary and provider data. The sample was restricted to adults aged 65 to 99 years. Measures of chiropractic availability and use were described and selectively mapped by state. Geographic variations were quantified. Spearman test was used to evaluate for correlation between chiropractic availability and use.
Results: The average number of doctors of chiropractic (DC) by state was 1135; average DC per 1000 beneficiaries was 2.5 (SD, 1.1). The average number of chiropractic users by state was 34 502 (SD, 30 844); average chiropractic users per 1000 beneficiaries was 76 (SD, 41). Chiropractic availability by state varied 6-fold, and chiropractic use varied nearly 30-fold. Availability was strongly correlated with use (Spearman ρ, 0.86; P < .001). Expenditures per DC were highest in the upper Midwest and lowest in the far West; expenditures per user were highest in New England and New York, and lowest in the West.
Conclusion: Chiropractic availability and use by older adults under Medicare predominated in rural states in the North Central United States. Expenditures were higher in the East and Midwest and lower in the far West. Chiropractic availability and use by state were highly correlated. Future analyses should use small-area analysis and statistical modeling to identify factors predictive of chiropractic use.
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