HOMEWORK #7 ANSWERS

Chapter 10

2. (a) 112. Work: 115 is 1 SD above average at age 18, so the estimate at age 35 is above average by r SDs. This is 0.8 x 15 = 12 points.

(b) 112. See section 3.

4. (a) 15 years.

(b) 13.5 years.

(c) Appearances are deceiving; all that is going on here is the regression effect (section 5).

Chapter 11

3. (a) x 2.5 = 1.5 inches.

(b) x 1.7 » 1.0 inches.

6. No. The conclusion seems right, but does not follow from the data. It could be, for example, that better students spend more time doing homework anyway.

7. Option (iii) is right: regression effect.

Chapter 12

2. Predicted income is ($960 per inch) x height-$37,400. Taller people make more money, on average. Probably, this reflects other variables in family background; although looking every inch an executive may not hurt.

7. The slope has to be 0.5, because the regression line has to go through the point of averages.

11. Something is wrong with the equation. The regression line has to go through the point of averages. This line doesn't.