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STAT 350 Lab 3
Due Friday Mar 4, 2011
Purposes:
Confidence Intervals
When turning in labs:
a) Please include your
NAME, CLASS TIME, AND THE LAB #
on your submission.
b) Label each part with the problem number and put them in logical order.
c) ALWAYS include your SAS code for each problem.
Part I
–
SAS Learning Code
A)
Confidence intervals for the mean:
proc ttest
stands for the t test procedure.
The confidence level C (e.g. 95%) cannot not be specified directly in
SAS. We must specify
alpha
which relates to the confidence as such, alpha = 1 – C.
For example, for 95%
confidence level, we specify alpha = 0.05.
SAS Learning code:
proc
ttest
data
=dataset
alpha
=
0.05
;
var
score;
run
;
/*Generates a 95% confidence interval for the mean score*/
SAS Learning output (look for the bolded part):
The TTEST Procedure
Statistics
Lower CL
Upper CL
Lower CL
Upper CL
Variable
N
Mean
Mean
Mean
Std Dev
Std Dev
Std Dev
Std Err
score
21
87.3
93.667
100.03
10.701
13.987
20.198
3.0522
So the 95% C.I. for μ is (87.3, 100.03).
Problem 1
Use the data contained in the file dogs.txt, which contains the weights in pounds of a random sample of some
dogs, to answer the following questions:
a)
Generate a QQplot to verify that the data is at least “roughly” normal.
(It is supposed to be for the small
sample t confidence interval to be valid.)
b)
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 Spring '08
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