12.24 d¼ 0 :196, almost 20%.
12.25 y¼
lnð 0 : 6 Þ
lnð 0 : 7 Þ
¼ 1 : 432
d¼ð 1 : 96 þ 0 : 84 Þ^2
1 þ 1 : 432
1 1 : 432
2
¼249 events
N¼
ð 2 Þð 249 Þ
2 0 : 6 0 : 7
¼710 subjects or 355 per group
12.26 y¼
lnð 0 : 4 Þ
lnð 0 : 5 Þ
¼ 1 : 322
d¼ð 1 : 96 þ 0 : 84 Þ^2
1 þ 1 : 322
1 1 : 322
2
¼408 events
N¼
ð 2 Þð 408 Þ
2 0 : 4 0 : 5
¼742 subjects or 371 per group
12.27 y¼
lnð 0 : 4 Þ
lnð 0 : 6 Þ
¼ 1 : 794
d¼ð 1 : 96 þ 0 : 84 Þ^2
1 þ 1 : 794
1 1 : 794
2
¼98 events
N¼
ð 2 Þð 98 Þ
2 0 : 4 0 : 6
¼98 subjects or 49 per group
12.28 p 1 ¼ 0 :18:(a)N¼590, 245 cases and 245 controls;(b)N¼960, 192
cases and 768 controls;(c)m¼66 discordant pairs andM¼271 case–
control pairs.
528 ANSWERS TO SELECTED EXERCISES