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May 17, 1965

Computing the Length of Survival in Long-Term Disease: A Methodological Note With Special Reference to Polycythemia Vera

Author Affiliations

From the Department of Chronic Diseases, Johns Hopkins University School of Hygiene and Public Health, Baltimore. Dr. Modan is now at the Tel-Hashomer Hospital, Israel.

JAMA. 1965;192(7):609-612. doi:10.1001/jama.1965.03080200027007

Any evaluation of survival data is subject to numerous pitfalls. A comparison of two groups of patients with polycythemia vera, one group treated by 32p and the second receiving treatment other than radiation, demonstrated that several incidental factors, mainly the lapse of time between the diagnosis and the onset of treatment, influenced the pattern of survival in a number of series of cases reported in the literature. This lead to the erroneous conclusion that the length of survival for patients treated with 32p is considerably greater than of those not so treated. After an adjustment for these factors was made, the pattern of survival of the two groups became similar.

These findings serve to stress the possible bias in interpreting survival data of retrospective case-control studies, unless the same base line is used for the two groups under consideration.