title: A longitudinal study of chiropractic use among older adults in the United States.
abstract: BACKGROUND
  Longitudinal patterns of chiropractic use in the United States, particularly among Medicare beneficiaries, are not well documented. Using a nationally representative sample of older Medicare beneficiaries we describe the use of chiropractic over fifteen years, and classify chiropractic users by annual visit volume. We assess the characteristics that are associated with chiropractic use versus nonuse, as well as between different levels of use.
  
  
  METHODS
  We analyzed data from two linked sources: the baseline (1993-1994) interview responses of 5,510 self-respondents in the Survey on Assets and Health Dynamics Among the Oldest Old (AHEAD), and their Medicare claims from 1993 to 2007. Binomial logistic regression was used to identify factors associated with chiropractic use versus nonuse, and conditional upon use, to identify factors associated with high volume relative to lower volume use.
  
  
  RESULTS
  There were 806 users of chiropractic in the AHEAD sample yielding a full period prevalence for 1993-2007 of 14.6%. Average annual prevalence between 1993 and 2007 was 4.8% with a range from 4.1% to 5.4%. Approximately 42% of the users consumed chiropractic services only in a single calendar year while 38% used chiropractic in three or more calendar years. Chiropractic users were more likely to be women, white, overweight, have pain, have multiple comorbid conditions, better self-rated health, access to transportation, higher physician utilization levels, live in the Midwest, and live in an area with fewer physicians per capita. Among chiropractic users, 16% had at least one year in which they exceeded Medicare's "soft cap" of 12 visits per calendar year. These over-the-cap users were more likely to have arthritis and mobility limitations, but were less likely to have a high school education. Additionally, these over-the-cap individuals accounted for 58% of total chiropractic claim volume. High volume users saw chiropractors the most among all types of providers, even more than family practice and internal medicine combined.
  
  
  CONCLUSIONS
  There is substantial heterogeneity in the patterns of use of chiropractic services among older adults. In spite of the variability of use patterns, however, there are not many characteristics that distinguish high volume users from lower volume users. While high volume users accounted for a significant portion of claims, the enforcement of a hard cap on annual visits by Medicare would not significantly decrease overall claim volume. Further research to understand the factors causing high volume chiropractic utilization among older Americans is warranted to discern between patterns of "need" and patterns of "health maintenance".
authors.affiliation: Department of Health Management and Policy, College of Public Health, the University of Iowa, Iowa City, Iowa, USA. jason-hockenberry@uiowa.edu.
authors.forename: Paula
authors.initials: P
authors.lastname: Weigel
authors.forename: Jason M
authors.initials: JM
authors.lastname: Hockenberry
authors.forename: Suzanne E
authors.initials: SE
authors.lastname: Bentler
authors.forename: Maksym
authors.initials: M
authors.lastname: Obrizan
authors.forename: Brian
authors.initials: B
authors.lastname: Kaskie
authors.forename: Michael P
authors.initials: MP
authors.lastname: Jones
authors.forename: Robert L
authors.initials: RL
authors.lastname: Ohsfeldt
authors.forename: Gary E
authors.initials: GE
authors.lastname: Rosenthal
authors.forename: Robert B
authors.initials: RB
authors.lastname: Wallace
authors.forename: Fredric D
authors.initials: FD
authors.lastname: Wolinsky