To obtain data on utilization and expenditures on U.S. chiropractic care, we analyzed data from the Medical Expenditure Panel Survey (MEPS) from 1997 to 2006 (The Medical Expenditure Panel Survey, Agency for Health Care Policy and Research 2009
). Annually conducted by the Agency for Health Care Policy and Research, the MEPS is a nationally representative survey of the noninstitutionalized U.S. population. Information is gathered on health care utilization, expenditures, health status, and visits to health care providers. The MEPS utilizes an overlapping panel design consisting of a household component, medical provider component, and insurance provider component. Each respondent is interviewed five times over a
time period, and a sample of medical providers and health care insurance providers are contacted to acquire additional information. For each year, personal and family-level data obtained from the household, medical provider, and insurance provider are aggregated and converted to annual estimates by MEPS statisticians. National estimates are calculated by the application of sample weights to reflect the participant's probability of selection and to account for sampling methodology.
We analyzed data from all respondents to the MEPS survey from 1997 to 2006. The MEPS utilizes a sample frame of the previous year's National Health Interview Survey to ensure a national representative sample frame. Sample sizes for the MEPS from 1997 to 2006 range from a low of 22,953 individuals in 1998 to a high of 32,737 in 2003; response rates ranged from 58.3 percent in 2006 to 66.8 percent in 1997. Respondents to the MEPS survey were asked if they had seen a chiropractor in the past 6 months and, if so, how many visits were made to the chiropractor and how much was spent on chiropractic care. If the individual reported having seen a chiropractor, the MEPS would then proceed to contact the individuals' chiropractor and health care insurance provider to verify information regarding utilization (i.e., visit dates and details of office-based or outpatient visits), charges, and expenditures. We restricted our analyses to U.S. adults (≥18 years) because the vast majority of chiropractic patients in the United States are adults (Cherkin et al. 2002
; National Board of Chiropractic Examiners 2005
;). The number of MEPS adult respondents who reported having seen a chiropractor ranged from 789 in 1997 to 1,082 in 2006.
We examined demographic data for individuals who had reported having visited a U.S. chiropractor in 1997 and 2006, including age, gender, race, health care insurance type, income, and education. We aggregated respondent self-reported race from the six categories reported by MEPS into “white,”“black,” and “other/multiple.” Health care insurance variables were combined for each corresponding year into “any private,”“public,” and “uninsured” categories. Census regions consisted of “northeast,”“midwest,”“south,” and “west.”
The U.S. Census Bureau differentiates U.S. regions by population density. Areas that are considered “metropolitan and micropolitan statistical areas” (MSAs) are defined by a core population of 50,000 or more (metropolitan) or a micropolitan population of 10,000 or more (U.S. Census Bureau 2009
). We report the proportion of chiropractic patients residing in MSAs.
Expenditures, Charges, and Visits to U.S. Chiropractors
We used the MEPS consolidated data files from years 1997–2006 to acquire information on the number of visits, expenditures, and charges annually and per visit to U.S. chiropractors. Charges were defined as the total amount billed for a health care service, while expenditures were the amounts actually paid by either the patient or their health care insurer. The MEPS distinguishes ambulatory visits to medical providers as either office-based or outpatient. Outpatient is defined as an ambulatory visit to a hospital and office-based are visits to health care provider offices. To estimate the total number of ambulatory visits to chiropractors, charges, and expenditures, we combined office-based and outpatient statistics. In addition, we extracted charges and expenditures on U.S. medical physician office-based encounters per patient and per visit over the same time period for comparison purposes.
We conducted descriptive analyses of the datasets using complex survey analysis methods. All analyses were conducted using STATA
version 10.0 statistical software (College Station, TX). To create real estimates of professional health care charges and expenditures, we converted all data to 2006 dollars using the Consumer Price Index for professional medical services provided by the U.S. Bureau of Labor Statistics (2008)
. We used the annual average Consumer Price Index for all urban workers to convert the 1997 income of chiropractic patients to 2006 dollars.
In order to determine the relative amount spent on chiropractic care among individuals who use the service, we calculated the fraction of total office-based expenditures on chiropractic care. The fraction of total office-based expenditures on chiropractic care excluded the small portion of chiropractic services rendered in outpatient hospital settings.
We also calculated the fraction of total health care expenditures (inpatient, outpatient, office-based, and medical prescription expenditures) on ambulatory chiropractic services (both office-based and outpatient expenditures combined) among those respondents who reported using chiropractic care.