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# ECON 15A Study Guide - Midterm Guide: Trail Of Broken Treaties, Scatter Plot, Standard DeviationExam

Department
Economics
Course Code
ECON 15A
Professor
Paul Shirey
Study Guide
Midterm

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NAME: _________________________________ I.D.: _____________________________________
TEST FOUR
PROBABILITY AND STATISTICS, ECON 15A
NOVEMBER 20, 2015
1. Is it possible for two variables to have a strong association, but the correlation coefficient fails to measure it? Please explain.
2. In a scatter diagram, which points have the greatest say in determining the direction and strength of the association?
3. Is it possible for the covariance to be positive, yet the correlation coefficient is negative? Please explain.
4. Let’s say that the correlation between hours studied and test score is 0.5 for UCI students. Let’s say that the correlation between
hours studied and test score is 0.4 for Cal State Fullerton students. UCI students score higher and study more than Cal State Fullerton
students. For the combined groups, is the correlation for between hours studied and test score most likely to be A) less than 0.4;
B) between 0.4 and 0.5; C) greater than .5. There is no need to explain.
5 6. (Two questions twenty points) There are five people with the below heights and weights. Please calculate the correlation
coefficient. YOU MUST SHOW ALL YOUR WORK
Andy 65 inches 150 pounds
Beth 64 inches 100 pounds
Carl 65 inches 160 pounds
Diane 67 inches 160 pounds
Edgar 69 inches 180 pounds
7. True or false and explain: If the covariance of two variables equals zero, then they are independent.
8. There is a game. If you play it, there is a 50% chance that you will lose \$2. There is a 25% chance that you will lose \$8. There is a
25% chance that you will win \$16. If you play it 25 times, how much do you expect to win (or lose)? Show ALL your work.
9. Lets continue with the game described in question 8. You play the game 25 times, what is the standard deviation of the amount
won (or lost)? Show ALL your work.
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