Math 243 Exam 2

Preparation

In regression what is considered an influential point?Any ordered pair is considered influential, if when removed, the result is that the calculation(maybe the regression equation) has dramatically changed.

Determining Tree Height

0

5

10

15

20

25

0 10 20 30 40

Diameter

Tre

e H

eig

ht

Which of the points shown could be a possible influential point?

Determining Tree Height

0

5

10

15

20

25

0 10 20 30 40

Diameter

Tre

e H

eig

ht

Which of the points shown could be a possible influential point?

Are influential points and outliers the same?

No!

See page 162 of your textOutliers, are points that lie outside the overall pattern of the other observations.

-6

4

14

24

34

44

0 10 20 30 40 50 60 70

Consider the following scatterplot.

Which point is an influential point and which are outliers.

y = 0.4472x + 9.7547

R2 = 0.6077

05

101520253035404550

-10 10 30 50 70

y = 0.5725x + 7.8088

R2 = 0.9006

05

101520253035404550

-10 10 30 50 70

y = 0.4607x + 9.7441

R2 = 0.66110

10

20

30

40

50

-10 10 30 50 70

y = 0.1747x + 14.554

R2 = 0.134305

101520253035404550

-10 10 30 50 70

What does strength refer to?

The strength of a relationship is determined by how close the points in the scatterplot lie to a simple form such as a line.

0

0.2

0.4

0.6

0.8

1

1.2

15 17 19 21 23 25

By what you can see on the graph, out of the choices given, which is closer to the actual correlation value, r.

a. -.89 b. .29 c. .77 d. 1

0

0.2

0.4

0.6

0.8

1

1.2

15 17 19 21 23 25

By what you can see on the graph, out of the choices given, which is closer to the actual correlation value, r.

a. -.89 b. .29 c. .77 d. 1

If r is very high like .91, does this mean that the explanatory variable causes a change in the response variable?

No! It just means that there is a strong linear association.

What does confounding of two variables mean?

When we can not distinguish the affects of the explanatory variable and the lurking variable on the response variable.

Which of the following calculations describe how the residual is calculated.

A. The mean of the response variables minus the observed value.

B. The observed value minus the predicted value.

C. The predicted value minus the mean of the explanatory variables.

True or False. The correlation, r, is a resistant measure.

False! The calculation for r involves the mean values which are also not resistant.

You will receive a good grade on the next exam by

A. Waiting until Sunday night to study.

B. Hoping for the best.

C. Paying a statistician to take the exam for you.

D. Review the vocabulary for the chapter. Attempt problems from the text. Review homework. Get together with other students to study.

Study Hard!

The End