BACKGROUND. Policymakers question whether there is a relationship between t
he number and distribution of physicians and the outcomes for important hea
lth conditions. We hypothesized that increasing primary care physician supp
ly would be related to earlier detection of colorectal cancer.
METHODS. We identified incident cases of colorectal cancer occurring in Flo
rida in 1994 (n = 8933) from the state cancer registry. We then obtained me
asures of physician supply from the 1994 American Medical Association Physi
cian Masterfile and examined the effects of physician supply (at the levels
of county and ZIP code clusters) on the odds of late-stage diagnosis using
multiple logistic regression.
RESULTS. For each 10-percentile increase in primary care physician supply a
t the county level, the odds of late-stage diagnosis decreased by 5% (adjus
ted odds ratio [OR] = 0.95; 95% confidence interval [CI], 0.92 - 0.99; P =
.007). For each 10-percentile increase in specialty physician supply, the o
dds of late-stage diagnosis increased by 5% (adjusted OR = 1.05; 95% Cl, 1.
02 - 1.09; P = .006). Within ZIP code clusters, each IO-percentile increase
in the supply of general internists was associated with a 3% decrease in t
he odds of late-stage diagnosis (OR = 0.97; 95% Cl, 0.95 - 0.99; P = .006),
and among women, each 10-percentile increase in the supply of obstetrician
/gynecologists was associated with a 5% increase in the odds of late-stage
diagnosis (OR = 1.05; 95% Cl, 1.01 -1.08; P =.005).
CONCLUSIONS. If the relationships observed were causal, then as many as 874
of the 5463 (16%) late-stage colorectal cancer diagnoses are attributable
to the physician specialty supply found in Florida. These findings suggest
that an appropriate balance of primary care and specialty physicians may be
important in achieving optimal health outcomes.