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Unformatted text preview: Homework ChS—Q Solutions Chapter 8 1. Diagram (d) is the right answer. (a) has a point average (50,50), (b) has small SDs, and
{d} has large SDs. 2. (a) Negative because the higher is the age of the car, the lower is its mileage per gallon.
(b) People with high income own new cars and maintain them better. 4. The correlation is 0.3, because there is a lot of variation around the SD line. 5. There is a positive correlation between GPAs in freshman year and sophomore year, and
between freshman year and senior year, but the correlation is weaker for the latest. The
answer is (i]0.6, (i003, and (iii]0.95. 8. (a)42 inches, (b)‘2.5 inches [about 95% are within 2 8135), (e)0.8, and (d}solid line. 10. If you draw vertical stripes at 75 and 125, there will be a lot more spread at 125, so the
prediction errors are smaller when the score is 75. 11. The correlation is r 2 H1. This is like the coin toss example done in class on the
correlation between the number of heads and tails. Chapter 9. 2. a. False. The cloud of points sloiies down. b. False. Take for example the heights at age 12 as your Y variable, and heights at age 20
as your X variable. 8. False. These are crosssectional data, not longitudinal. Younger people were born later
and educational levels have been going up ever time. 11. Less than 0.9T, see Section 4 on ecological correlations. 12. a. Educational level is measured in whole years. b. Some dots correspond to couples with the same educational level. Ci (11(0). (110(3). (NRA) Homework 01189 Solutions Chapter 8 1. Diagram (d) is the right answer. (a) has a point average (50,50), (1)] has small SDs, and
(d) has large SDs. 2. (a) Negative because the higher is the age of the car, the lower is its mileage per gallon.
(13) People with high income own new cars and maintain them better. 4. The correlation is 0.3, because there is a lot of variation around the SD line. 5. There is a positive correlation betwee
between freshman year and senior year,
answer is (00.6, (ii]0.3, and {iii)0.95. n GPAs in freshman year and sophomore year. and
but the correlation is iveaker for the latest. T he 8. (a}42 inches, {b)2.5 inches (about 95% are within 2 8135], (c)0.8, and (d]solid line. 10. If you draw vertical stripes at 75 and 125, there will be a lot more spread at 125, so the
prediction errors are smaller when the score is 75. Chapter 9. 2. 51. False. The cloud of points sloiies down. b. False. Take for example the heights at age 12 as your Y variable, and heights at age 20
as your X variable. 8. False. These are cross—sectional data, not longitudinal. Younger people were born later
and educational levels have been going up ever time. 11. Less than 0.97, see Section 4 on ecological correlations. 12. 3. Educational level is measured in whole years. b. Some dots correspond to couples with the same educational level. C (1)03), (iii}(B}= (iVHAl ...
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 Spring '08
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 Correlation, Correlation and dependence, Sophomore's dream, educational level, 2.5 inches

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