Objective: There is controversy as to whether increased doctor-patient ratios result in a commensurate benefit to the health care consumer. This study assesses doctor (allopathic/osteopathic physician and chiropractor) ratios in the 50 states in the United States and correlates these ratios with various health outcomes to determine if one doctor type has stronger correlations in certain outcomes compared with the other doctor type by geographic region.

Methods: A total of 21 health outcomes for the year 2004, such as obesity and cancer deaths, were correlated with 2004 physician and chiropractor ratios (number of doctors per 100000 population). The 25 highest doctor ratio states, along with the corresponding health outcomes, were compared with the 25 lowest doctor ratio states and the corresponding health outcomes. The Spearman and Wilcoxon tests (for correlation and differences, respectively) were used to assess the data.

Results: Increases in doctor ratios resulted in correlations in 12 outcomes for chiropractors and 8 outcomes for allopathic/osteopathic physicians. When comparing low with high doctor ratios, physicians had improvements in 13 outcomes, whereas chiropractors had 12.

Conclusions: Correlation does not necessarily show causation but may provide clues. Many of the improved outcomes were not surprising for allopathic/osteopathic physicians, for example, cardiovascular deaths, but were surprising for chiropractors. It is possible, although care should be taken to avoid overspeculation, that doctors of chiropractic are having an effect in seemingly unlikely outcomes such as cardiovascular and cancer deaths. Further research is warranted for other years to verify these findings.