1. Math 243 Exam 2
Preparation

2. 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.

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

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

5. Are influential points and outliers the same?
No!
See page 162 of your text
Outliers, are points that lie outside the overall pattern of the other observations.

6. Consider the following scatterplot.
Which point is an influential point and which are outliers.

8. 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.

9. By what you can see on the graph, out of the choices given, which is closer to the actual correlation value, r.
a b c d. 1

10. By what you can see on the graph, out of the choices given, which is closer to the actual correlation value, r.
a b c d. 1

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

12. 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.

13. 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.

14. True or False. The correlation, r, is a resistant measure.
False! The calculation for r involves the mean values which are also not resistant.

15. 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.

16. Study Hard!
The End