11.5 Data are shown in Table 11.3 for two groups of patients who died of
acute myelogenous leukemia (see Example 11.3). Patients were classi-
fied into the two groups according to the presence or absence of a
morphologic characteristic of white cells. Patients termed AG positive
were identified by the presence of Auer rods and/or significant gran-
ulature of the leukemic cells in the bone marrow at diagnosis. For AG-
negative patients these factors were absent. Leukemia is a cancer char-
acterized by an overproliferation of white blood cells; the higher the
white blood count (WBC), the more severe the disease. Calculate and
graph in the same figure the two Kaplan–Meier curves (one for AG-
positive patients and one for AG-negative patients). How do they
compare?
11.6 In Exercise 11.4 we described a diet study, and tumor-free times were
given for the 30 rats fed an unsaturated-fat diet. Tumor-free times
(days) for the other two groups are as follows:
Low-fat: 140, 177, 50, 65, 86, 153, 181, 191, 77, 84, 87, 56, 66, 73,
119, 140þ, and 14 rats at 200þ
Saturated-fat: 124, 58, 56, 68, 79, 89, 107, 86, 142, 110, 96, 142, 86,
75, 117, 98, 105, 126, 43, 46, 81, 133, 165, 170þ, and 6 rats at 200þ
(140þ and 170þ were due to accidental deaths without evidence of
tumor). Calculate and graph the two Kaplan–Meier curves, one for rats
fed a low-fat diet and one for rats fed a saturated-fat diet. Put these two
curves and the one from Exercise 11.4 in the same figure and draw
conclusions.
11.7 Consider the data shown in Table E11.7 (analysis date, 01/90; A, alive;
D, dead). For each subject, determine the time (in months) to death (D)
or to the ending date (for survivors whose status was marked as A);
then calculate and graph the Kaplan–Meier curve.
TABLE E11.7
Subject Starting Ending Status (A/D)
1 01/80 01/90 A
2 06/80 07/88 D
3 11/80 10/84 D
4 08/81 02/88 D
5 04/82 01/90 A
6 06/83 11/85 D
7 10/85 01/90 A
8 02/86 06/88 D
9 04/86 12/88 D
10 11/86 07/89 DEXERCISES 427