FROM: J Manipulative Physiol Ther. 2014 (Oct); 37 (8): 542-551 ~ FULL TEXT
Paula A.M. Weigel, PhD, Jason M. Hockenberry, PhD, Fredric D. Wolinsky, PhD
Department of Health Management and Policy,
College of Public Health,
The University of Iowa, Iowa City, IA.
OBJECTIVE: The purpose of this study was to examine how chiropractic care compares to medical treatments on 1-year changes in self-reported function, health, and satisfaction with care measures in a representative sample of Medicare beneficiaries.
METHODS: Logistic regression using generalized estimating equations is used to model the effect of chiropractic relative to medical care on decline in 5 functional measures and 2 measures of self-rated health among 12170 person-year observations. The same method is used to estimate the comparative effect of chiropractic on 6 satisfaction with care measures. Two analytic approaches are used, the first assuming no selection bias and the second using propensity score analyses to adjust for selection effects in the outcome models.
RESULTS: The unadjusted models show that chiropractic is significantly protective against 1-year decline in activities of daily living, lifting, stooping, walking, self-rated health, and worsening health after 1 year. Persons using chiropractic are more satisfied with their follow-up care and with the information provided to them. In addition to the protective effects of chiropractic in the unadjusted model, the propensity score results indicate a significant protective effect of chiropractic against decline in reaching.
CONCLUSION: This study provides evidence of a protective effect of chiropractic care against 1-year declines in functional and self-rated health among Medicare beneficiaries with spine conditions, and indications that chiropractic users have higher satisfaction with follow-up care and information provided about what is wrong with them.
From the Full-Text Article:
National surveys and other data show chiropractic use prevalence rates among those 18 years and older, ranging between 5.6% and 8.6% in the United States. [1-3] Among Medicare beneficiaries 70 years and older, chiropractic use is less prevalent, with 2 studies indicating annual rates ranging between 4.1% and 5.4%. [4, 5] For younger Medicare beneficiaries, chiropractic prevalence rates are closer to national rates, ranging between 6% and 7%.  Although informative, these estimates are not reflective of the population that commonly seeks care from doctors of chiropractic — namely, persons seeking treatment of spine-related health conditions. [2, 7-9] Prevalence of chiropractic use is likely higher in the population of Medicare beneficiaries with back and neck conditions, but how much higher is not known.
Spine-related problems are common in the general adult population, and there is evidence of increasing prevalence as people age. [10-14] As a result, spine conditions reflect a growing portion of health services use and expenditures, particularly under Medicare. [6, 15, 16] More significantly, these problems are associated with increased disability by impeding a person's capacity to perform everyday mobility tasks such as walking, stooping, lifting, or reaching. Those mobility tasks can subsequently limit a person's ability to perform basic activities of daily living (ADLs), all of which are crucial to prolonging independence among older adults living in a community setting. [17-22]
Medicare covers several treatment options ranging from the noninvasive like chiropractic and physical therapy to the more invasive, such as steroidal injections and surgery. Studies have shown that the technologically intensive treatment types have grown more dramatically, both in use and in expenditures, than the noninvasive kind over the past 15 to 20 years. [3, 6, 12, 16, 23-26] Although these studies document the increasing use of interventional treatments, they also note that population-level improvements in outcomes and disability have not improved commensurately.
Recent research, however, suggests that chiropractic use benefits older Medicare beneficiaries (>70 years) by protecting them against decline in function and self-rated health (SRH).  Because that study used Medicare claims to compare outcomes between users of chiropractic and users of medical care treatments in uncomplicated back conditions over a 2-year period, it represents a real-world approximation of the relative benefit of chiropractic use on health outcomes.
Given the escalating costs of treatment and the ramifications of disability on future dependency, [28, 29] it is important to understand the prevalence and the relative effect on health and care, costs of chiropractic use among age-eligible Medicare beneficiaries with spine-related problems. Equally important is how patients view the quality of care received from different treatment types. If treatments have comparable effects on health, but disparate care costs or satisfaction, then policy makers may consider incentives or disincentives to promote particular treatments for certain conditions.
This study uses the Medicare Current Beneficiary Survey (MCBS) linked to Medicare provider claims to examine chiropractic use among Medicare beneficiaries with spine conditions. This research study has 3 objectives:
(1) to describe the prevalence of chiropractic use among age-eligible Medicare beneficiaries in general and among those with spine problems in particular;
(2) to describe treatment patterns, service trends, and Medicare expenditures among persons who mostly use chiropractic vs those that are users of medical care only; and
(3) to determine the comparative effect of chiropractic relative to medical care only on 1-year changes in function, self-rated health (SRH), and satisfaction with care.
We investigated chiropractic use among community-dwelling age-eligible Medicare beneficiaries over a 9-person-year period (1997-2006). We found annual prevalence rates similar to those reported from the National Health Interview Surveys. [1, 2] Our prevalence estimates for chiropractic use among beneficiaries with spine diagnoses, however, are much higher (35%), indicating that chiropractic is a commonly sought treatment among those with back and neck problems. Furthermore, chiropractic users appear to have strong preferences for chiropractic treatment once they choose chiropractic compared with other types of services based on the percent of overall service volume for chiropractic relative to other care, although the data on provider mix suggest a trend toward service provision by others.
Service volume trends were similar between treatment groups, with average yearly service volume steadily increasing between the 1997 to 1998 panel and the 2005 to 2006 panels. On a percentage basis, however, service volume in the medical only group grew slightly more between the 1997 to 1998 panel and the 2005 to 2006 panel (58% vs 41% for the chiropractic use group). Chiropractic volume grew at a lesser rate than the overall average volume, and consequently, chiropractic volume as a percentage of all services used to treat spine conditions declined over time (from 90% in 1997-1998 to 78% in 2005-2006). This trend is also evident in the distribution of provider data, where a growing proportion of services among the chiropractic use group went to physical therapists.
As a byproduct of the service volume growth and differences in prices between general and specialty care, average spending per year by Medicare also increased between the first and last panels in both groups. Once again, this occurred at a faster rate in the medical only group relative to the chiropractic user group (117% vs 74%, respectively). Furthermore, the percent growth in average chiropractic spending per year from 1997-1998 to 2005-2006 was only 6%, which is remarkably lower than the growth in overall spending in each group. Inflation-adjusted spending on chiropractic was essentially flat over the period and was accompanied by a declining portion of total spending among persons using chiropractic (from 79% to 48% in 1997-1998 and 2005-2006, respectively). In support of conclusions by Whedon et al.  about trends in use and costs of chiropractic spinal manipulation in the Medicare population, our results suggest Medicare payments for chiropractic services (at least among those with spine conditions) are relatively less of a payment vulnerability for the Medicare program than has been implied in the past. 
We found that chiropractic use is comparatively protective against 1-year declines in function and self-assessed health among Medicare beneficiaries with spine conditions and is also associated with higher satisfaction on measures of follow-up care and with information provided. Furthermore, we found that the models measuring the effect of chiropractic on functional health, self-rated health (SRH), and satisfaction with care using IPTWs are consistent with the models that are not adjusted for potential selection to treatment. By using propensity score methods, we accounted for potential selection bias using the data available. In so doing, we demonstrated that the causal effects using IPTWs were similar to those observed without such adjustments.
Limitations and Future Research
The decision to combine back and neck conditions in these analyses introduces clinical condition heterogeneity that could make indistinguishable the comparative effect of chiropractic on health changes for certain specific conditions. However, we felt that expanding the number and types of conditions for which people consistently choose chiropractic was important to the overall picture of how chiropractic is used in this population.
We did not aggregate service use into episodes of care but rather looked at overall service use and spending over the course of a year. Whether chiropractic treatment is comparatively effective at slowing functional decline is a function of how it is delivered in practice for a particular clinical presentation. Evidence of chiropractic efficacy has shown a minimally effective “dosing” level of up to 12 treatments over a several week period, with some studies suggesting that an additional monthly treatment thereafter prolongs the benefit. [44-46] Combining related service claims into episodes of care could further refine treatment effect estimates, although it would likely introduce analytical complexity due to care that is proximal but outside the 1-year interview window (left and right censoring).
Another limitation is related to the satisfaction with care outcomes. Questions regarding satisfaction in the MCBS are not specific to a particular treatment delivered for an identifiable health condition but rather are about the medical services received since the time of the last interview. Accordingly, a distinction cannot be made between health services delivered for a back condition vs those delivered for a heart condition. Persons seeking treatment of spine conditions had health services use for other conditions as well, thus confounding satisfaction perceptions across a variety of providers. Had the questions been related only to care received for spine conditions, a better distinction between treatment groups could be made.
Despite attempts to adjust for potential selection bias using IPTWs, it remains possible that unobserved confounders affected the treatment effect on declines in health.
Future research will focus on distinguishing further among specific types of spine conditions to better determine the comparative effect of chiropractic relative to medical only care on the health and well-being of Medicare beneficiaries with specific clinical conditions.
This study found prevalence of chiropractic use among age-eligible Medicare beneficiaries consistent with that of the US adult population, but among those seeking care for spine problems, we observed a much higher prevalence rate. Service volume trends between 1997 and 2006 showed growth in the average number of services used to treat spine conditions, although the percentage growth of chiropractic services was nearly flat compared with overall service volume growth. Medicare spending on spine conditions grew as a consequence of higher service volume and more expensive services, although spending on chiropractic was relatively flat and declined as a percentage of total spending among those choosing chiropractic.
This study provides evidence of a protective effect of chiropractic against 1-year declines in functional and self-rated health (SRH) among Medicare beneficiaries with spine conditions, and indications that chiropractic users have higher satisfaction with follow-up care and information provided about what is wrong with them.