Table 2. Adjusted Rate Ratios* (95% Confidence Intervals) for the Association between Quintile of Chiropractic Care Supply and Annual Number of Visits to Primary Care Physicians for Back and/or Neck Pain
Independent VariableVisits to any PCP for back and/or neck painVisits for Back and/or Neck Pain, By PCP Specialty
Family Medicine PCPInternal Medicine PCP
Supply of health services
    Quintile of chiropractic care
        1 (lowest)1.00 (Reference)1.00 (Reference)1.00 (Reference)
        21.08 (1.07–1.09)1.07 (1.06–1.08)1.08 (1.07–1.09)
        30.98 (0.97–0.98)0.97 (0.96–0.98)0.94 (0.93–0.94)
        40.97 (0.97–0.98)0.86 (0.86–0.86)1.02 (1.01–1.02)
        5 (highest)0.92 (0.91–0.92)0.85 (0.84–0.86)0.90 (0.89–0.91)
    PCP services, number per 10,0001.00 (1.00–1.00)1.02 (1.02–1.02)1.01 (1.01–1.01)
Patient characteristics
    Age, years1.00 (0.99–1.00)0.99 (0.99–0.99)1.01 (1.00–1.01)
    Sex
        Male1.00 (Reference)1.00 (Reference)1.00 (Reference)
        Female1.36 (1.35–1.36)1.30 (1.30–1.31)1.41 (1.40–1.41)
    Race/ethnicity
        Non-Hispanic white1.00 (Reference)1.00 (Reference)1.00 (Reference)
        Other1.11 (1.10,–1.11)1.00 (0.99–1.00)1.15 (1.14–1.16)
    Rurality of residence
        Urban1.00 (Reference)1.00 (Reference)1.00 (Reference)
        Rural0.99 (0.99–0.99)1.39 (1.38–1.40)0.72 (0.71–0.72)
    Charlson Comorbidity Score
        01.00 (Reference)1.00 (Reference)1.00 (Reference)
        11.13 (1.12–1.13)1.10 (1.09–1.11)1.15 (1.14–1.16)
        21.25 (1.25–1.26)1.20 (1.19–1.21)1.30 (1.30–1.31)
        ≥31.29 (1.29–1.301.22 (1.21–1.24)1.35 (1.34–1.35)
  • For each of the 3 models, n = 14.9 million Medicare patients.

  • * All rate ratios are highly significant at P <.001 (except for race/ethnicity) in predicting visits to family medicine physicians.

  • Variable used corresponds to primary care physician (PCP) specialty for the respective model (eg, for prediction of visits to family medicine PCPs, number of family medicine physicians per 10,000 capita was used).