LINEAR REGRESSION MODELS W4315
HOMEWORK 3 ANSWERS
February 20, 2010
Instructor: Frank Wood
1. (50 points)
1
Refer to
Copier maintenance
Problem 1.20.
a.
Estimate the change in the mean service time when the number of copiers serviced
increases by one. Use a 90 percent confidence interval. Interpret your confidence interval.
b. Conduct a
t
test to determine whether or not there is a linear association between X and
Y here; control the
α
risk at .10. State the alternatives, decision rule, and conclusion. What
is the
P
value of your test?
c. Are your results in parts (a) and (b) consistent? Explain.
d. The manufacturer has suggested hat the mean required time should not increase by more
than 14 minutes for each additional copier that is serviced on a service call. Conduct a test
to decide whether this standard is being satisfied by TriCity. Control the risk of a Type I
error at .05. State the alternatives, decision rule, and conclusion. What is the
P
value of
the test?
e. Does
b
0
give any relevant information here about the ”startup” time on callsi.e., about
the time required before service work is begun on the copiers at a customer location?
Answer:
a. First read the data into Matlab and estimate the coefficients of the regression line
pr1=textread(’CH01PR20.txt’);
X=pr1(:,2);
Y=pr1(:,1);
avgX = mean(X);
avgY = mean(Y);
SXX
=
sum
((
X

avgX
)
.
2
);
SXY = sum((XavgX).*(YavgY));
b1 = SXY/SXX;
b0 = avgY b1*avgX;
1
This is problem 2.5 in ”Applied Linear Regression Models(4th edition)” by Kutner etc.
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 Fall '08
 Staff
 Statistics, Linear Regression, Regression Analysis, Linear Regression Models, Applied Linear Regression Models

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