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STAT 350 – Fall 2008
Lab #4
DUE:
Monday, October 20
th
@ the beginning of class
All the following analyses should be conducted using SAS.
For all tests, use a significance level of 0.05.
Attach the SAS input (editor window content) at the end of your assignment.
1.
The Survey of Study Habits and Attitudes (SSHA) is a psychological test that measures
students' study habits and attitude toward school.
Scores range from 0 to 200.
Higher scores
indicate better attitudes.
An educational psychologist believes that older students have a
better attitude toward school than younger students.
To test this theory, she gives the SSHA
test to 15 students with ages between 18 and 21 and to 7 students with ages between 30 and
40.
She brings the results of their tests (below) to you for help with the analysis.
young:
115
124
90
118
116
157
127
80
119
124
86
79
161
108
108
old:
116
122
127
131
122
119
122
a.
State the null and alternative hypotheses.
If you use subscripts, be clear to identify which
group is which.
H
0
:
μ
old

μ
young
= 0
H
a
:
μ
old

μ
young
> 0
b. Conduct a
t
test, and copy and paste the output of the analysis onto your assignment.
The TTEST Procedure
Statistics
Lower CL
Upper CL
Lower CL
Upper CL
Variable
age
N
Mean
Mean
Mean
Std Dev
Std Dev
Std Dev
Std Err
score
old
7
118.13
122.71
127.3
3.1942
4.957
10.916
1.8736
score
young
15
100.66
114.13
127.61
17.811
24.328
38.367
6.2814
score
Diff (12)
11.03
8.581
28.188
15.71
20.534
29.653
9.3993
TTests
Variable
Method
Variances
DF
t Value
Pr > t
score
Pooled
Equal
20
0.91
0.3722
score
Satterthwaite
Unequal
16.3
1.31
0.2087
Equality of Variances
Variable
Method
Num DF
Den DF
F Value
Pr > F
score
Folded F
14
6
24.09
0.0008
Lab #4
Page 1 of 6
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Is the assumption of equal variances appropriate?
Give both the appropriate
p
value and
your conclusion.
No, the assumption of equal variances is NOT appropriate.
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 Fall '08
 Staff

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