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1.
Plot the data for the two populations on the same graph, using different symbols (
v=
) and
lines. Does the relationship between speed and operating cost appear to be the same for
the two makes of tire?
No, the two lines appear to be quite different.
In particular they have different slopes, so that the
relationship between cost and speed is different for the two makes of tire.
2.
Examine the question of whether or not the two lines are the same. Write a model that
allows the two makes of tires to have different intercepts and slopes. Then, perform the
general linear test to determine whether the two lines are equal.
State the null and
alternative hypothesis, the test statistic with degrees of freedom, the Pvalue and your
conclusion.
01
12
23
3
YX
X
X
=β +β
+β
+
ε
where X
1
= make, X
2
= speed, and X
3
= X
1
X
2
, allows the two
makes of tire to have different intercepts and slopes.
For make A (make = 0) the intercept is
β
0
and and the slope is
β
2
.
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 Spring '08
 Staff

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