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Solutions to STAT 426 HW2.
2.8
Let
p
1
be the estimated probability that people who suﬀer fatal injuries in
car accident without wearing their seat belts, and
p
2
be the estimated proba
bility that people who suﬀer fatal injuries in car accident with wearing their
seat belts.
p
1
=
1601
1601+162527
= 0
.
009755
,p
2
=
510
510+412368
= 0
.
001235
The diﬀerence of proportions =
p
1

p
2
= 0
.
009755

0
.
001235 = 0
.
00852.
The sample probability that people who suﬀer fatal injuries in car accident
without wearing their seat belts is 0.00852 higher than the sample probabil
ity that people who suﬀer fatal injuries in car accident with wearing their
seat belts.
The relative risk
p
1
p
2
=
0
.
009755
0
.
001235
= 7
.
90
The sample probability that people who suﬀer fatal injuries in car accident
without wearing their seat belts is 7.9 times the sample probability that peo
ple who suﬀer fatal injuries in car accident with wearing their seat belts.
The odds ratio =
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This note was uploaded on 04/29/2010 for the course STAT stat 426 taught by Professor Xe during the Spring '10 term at University of Illinois at Urbana–Champaign.
 Spring '10
 Xe
 Probability

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