Homework 3 Solutions
6.11
a.
Percentage ever bullied = (42/92)
×
100% = 45.65% among short students
b.
Percentage ever bullied = (30/117)
×
100% = 25.64% among students not short
c.
Yes, there is a relationship.
Short students are more likely to have been bullied
than students who are not short.
6.23
a.
For short students, risk = 42/92 = .4565, or 45.65%.
For “not short” students, risk = 30/117 = .2564, or 25.64%.
b.
Relative risk =
78
.
1
64
.
25
65
.
45
category
short"
not
"
in
Risk
category
short"
"
in
Risk
=
=
.
Short students are 1.78 times as likely to be bullied as are students who are not
short.
c.
Percent increase in risk = (Relative risk
−
1)
×
100% = (1.78
−
1)
×
100% = 78%.
Equivalently,
%
78
%
100
64
.
25
64
.
25
65
.
45
%
100
risk
Baseline
risks
in
Difference
=
×
−
=
×
Being short increases the risk of being bullied by 78%.
d.
Odds ratio =
346
.
2
3448
.
8077
.
87
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 '08
 BARROSO,JOAOR
 Statistics, Null hypothesis, Statistical hypothesis testing, new treatment, short students

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