The attrition rate of licensed chiropractors in California: an exploratory ecological investigation of time-trend data

Abstract

Background: The authors hypothesized the attrition rate of licensed chiropractors in California has gradually increased over the past several decades. "Attrition" as determined for this study is defined as a loss of legal authority to practice chiropractic for any reason during the first 10 years after the license was issued. The percentage of license attrition after 10 years was determined for each group of graduates licensed in California each year between 1970 and 1998. The cost of tuition, the increase in the supply of licensed chiropractors and the ratio of licensed chiropractors to California residents were examined as possible influences on the rate of license attrition.

Methods: The attrition rate was determined by a retrospective analysis of license status data obtained from the California Department of Consumer Affairs. Other variables were determined from US Bureau of Census data, survey data from the American Chiropractic Association and catalogs from a US chiropractic college.

Results: The 10-year attrition rate rose from 10% for those graduates licensed in 1970 to a peak of 27.8% in 1991. The 10-year attrition rate has since remained between 20-25% for the doctors licensed between 1992-1998.

Conclusions: Available evidence supports the hypothesis that the attrition rate for licensed chiropractors in the first 10 years of practice has risen in the past several decades.

Figure 1

Percentage of license attrition, 1970-1998. A graphical depiction of the percentage of chiropractors without practice rights 10 years after the license was issued. The range was 10% in 1970 and a peak of 27.8% in 1991. The 10-year attrition rate has since remained between 20-25% for the doctors licensed between 1992-1998.

Figure 2

Percentage of yearly increase/decrease in chiropractors. The total number of licensed chiropractors decreased in 1971, 1972, 1973 and 1975, the largest drop of 3.9% occurring in 1972. The largest increase was 11.4% in 1985.

Figure 3

Increase in total population of California chiropractors by decade. A bar graph depicting the total increase in licensed chiropractors for each decade from 1970 to 2008.

Figure 4

Increase in licensed chiropractors, 1970-2008. The number of licensed chiropractors rose from 4306 in 1970 to 11,637 in 1998, a rise of 170.2%. The total number of active licenses has continued to rise and was 13,822 in 2008.

Figure 5

Yearly percentage change in California population and licensed chiropractors. The annual percentage of increase or decrease in California chiropractors from 1970 to 1998 was plotted with the solid line. The annual percentage growth in California residential population was plotted with the dashed line. The yearly percentage in licensed chiropractors exceeded the yearly percentage growth in population from 1977 until 1997. The disparity in growth rates reached its peak of 9% difference in 1985.

Figure 6

Change in the doctor/patient ratio. The calculated potential population for each licensed chiropractor, using 10% of the residential population, decreased from 534 patients per doctor in 1976 to 283 patients in 1998.

Figure 7

Changes in tuition 1970 to 1999. A time-trend depiction of the increasing quarterly tuition of a chiropractic college from 1970 to 1999. The dotted line represents the $255 per quarter tuition in 1970 adjusted for inflation between 1970 and 1999. The actual rise in tuition exceeds inflation by 414%.

Figure 8

ACA Survey data on gross and net income. The solid line represents ACA survey data on gross income in 1980, 1989, 1991 and 1997. The dashed line represents net income from the same survey.

Figure 9

ACA Survey data on gross and net income adjusted for inflation. The solid line represents inflation adjusted ACA survey data on gross income in 1980, 1989, 1991 and 1997. The dashed line represents inflation adjusted net income from the same survey. Note that the adjusted net income in 1997 has returned to the 1980 level.