The medical records of local patients are a unique resource for studies on the incidence of disease. This resource exists at the Mayo Clinic known as the Rochester Project.
The Rochester Project is a series of studies of the incidence and prevalence of disease, based on information drawn from the medical records of Rochester and Olmsted County patients dating back many decades.
During the 1970s, the Rochester Project, funded through grants from the National Institute of Health, completed more than 130 studies of various diseases. These included studies of leukemia, renal stones, prostate cancer, rheumatoid arthritis, fractures, and ischemic heart disease.
The foundation of the Rochester Project was Mayo patient records, dating back to the turn of the century. These histories contained records of Clinic and emergency room visits, hospitalizations, laboratory reports and causes of death, including autopsy results.
Although the limited size of the local population may pose a problem in the study of uncommon illnesses, the long period of coverage—from 20 to 60 years—provided Mayo researchers with a sizable population in terms of “person-years” of experience (number of persons multipled by number of years followed). A 40-year study, for example, represents about 2.5 million person-years of experience for the measurement of incidence rates.
Hundreds of lists of cases, grouped by diagnosis, were retrieved from the central index. The number of patient records extracted for each depended on the complexity of the research, the rarity of the disease, and the time span covered. Some investigations required data from several thousand patient files, while a few hundred records sufficed for other studies.