Impact of referral bias on evaluation of cataract surgery

Abstract

Patients from a defined population (Olmsted County, Minnesota) who underwent cataract extraction during 1980 were compared with referral patients operated on at the Mayo Clinic to determine whether selective referral of patients introduces bias into studies conducted at academic centers. Rates of cataract extraction in Olmsted County increased continuously with increasing age and, in the older groups, were greater among females than males. The overall age- and sex-adjusted annual rate, 120 per 100,000 population, was considerably lower than that for 1980 in the United States, 209 per 100,000 population. A significantly greater proportion of referral patients had coexistent diabetes mellitus (P