Distance bias and surgical outcomes.

BACKGROUND: A body of research has found that patients who travel a significant distance to obtain medical treatment experience better outcomes, a phenomenon termed "distance bias." This study uses risk-adjusted surgical outcomes data to analyze distance bias in a population of patients treated surgically at a tertiary care institution.
METHODS: We used risk-adjusted surgical outcomes data from the National Surgical Quality Improvement Project at the Mayo Clinic to calculate observed and expected risk of a severe complication. Operations were stratified into quintiles based on the distance traveled by the patient.
RESULTS: The average age of patients in our cohort was 56.7 years, and 59.2% were female; patients traveled an average of 226 miles for treatment. Patients living closest to the Mayo Clinic (quintile 1) had lower observed and expected risks of a severe complication relative to patients in quintiles 2-5. Patients from quintile 1 had outcomes which were better than predicted [observed:expected risk ratio of 0.82 (range, 0.63-0.99)]. Patients traveling intermediate distances (quintile 2) had outcomes which were worse than predicted [observed:expected risk ratio of 1.18 (range, 1.00-1.42)]. Operations performed on patients from greater distances (quintiles 3-5) had an observed risk of severe complications which was similar to expected. DISCUSSION: The phenomenon of distance bias which has previously been documented in medical and oncologic treatment is not demonstrated in this study. An opposite phenomenon may be more pertinent, where patients who are treated locally are less likely to have a severe complication and have outcomes which are better than predicted.