Maximum utilization of the life table method in analyzing survival.

44 EASUREMENT of patient survival is necessary for the evaluation of I treatment of usually fatal chronic diseases. This is particularly true for cancer. The American College of Surgeons, recognizing this, requires the maintenance of a cancer case registration and follow-up program for approval of a hospital cancer program.’ Acceptance of survival as a criterion for measuring the effectiveness of cancer therapy is also attested to by the very large number of papers published every year reporting on the survival experience of cancer patients. Although the proportion of patients alive 5 years after diagnosis (S-year survival rate) is the most frequently used index for measuring the efficacy of therapy in cancer, an increasing number of investigators are reporting on the manner in which patient populations are depleted during a period of time, e.g., survival curves. A popular and relatively simple technique for describing survival experience over time is known as the actuarial or life table method. Whereas the method and its uses have been admirably described by a number of authors,2-6 one important aspect has received relatively little attention. A principal advantage of the life table method is that it makes possible the use of all survival information accumulated up to the closing date of the study. Thus, in computing a S-year survival rate one need not restrict the material to only those patients who entered observation 5 or more years prior to the closing date. We will show that patients who entered observation 4, 3, 2, and even one year prior to the closing date contribute much useful information to the evaluation of 5-year survival. Let us consider a group of patients entering observation continuously beginning with Jan. 1, 1946. Sometime early in 1952, we decide to analyze the survival experience of these patients to obtain a 5-year survival rate. We choose Dec. 31, 1.951, as the closing date, i.e., the follow-up status and survival time of each patient is recorded as of that date.