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In Reply.–Ms Lang has made some important points. Tracing patients is in fact a difficult and time-consuming task. We are fortunate at the University of Iowa to have a very active Tumor Registry. The patients are contacted every six months the first two years and then once a year until death occurs; a death certificate is then obtained.
The number of patients "lost to follow-up" is an important factor if survival rates are calculated by the "direct method." To minimize the influence of such a source of error we used the "actuarial method." In this method, we deal with "person-years exposed to observation" rather than "persons." At present, we believe that the "actuarial method" gives a statistically better estimate of survival rates.
Shammas HF, Blodi FC. Lost to Follow-up-Reply. Arch Ophthalmol. 1977;95(6):1082. doi:10.1001/archopht.1977.04450060169027