x 2.5 = 1.5 inches.HOMEWORK #7 ANSWERS
Chapter 10
1. A (i) B (iii) C (ii)
3. (a) 64 inches. The husband is 4 inches, or 4/2.7 » 1.5 SDs above average in height. The wife is predicted to be above average in height by:
r x 1.5 = 0.25 x 1.5 » 0.4SDs.
This is 0.4 x 2.5 = 1 inch.
5. (a) False (unless there is something special about the SDs and the point of averages).
(b) False: r measures association not causation.
(c) True.
(d) True: the correlation between y and x equals the correlation between x and y.
(e) False: r measures association not causation.
6. Dashed: y on x.
Dotted: SD line.
Solid: x on y.
See section 5.
9. (a) 21% This student was 1.65 SDs below average on the midterm--
He should be r x 1.65 = 0.5 x 1.65 » 0.8 SDs below average on the final. Now for
the percentile rank on the final--21%
(b) 65% (c) 50% (d) 50%
Chapter 11
3. (a) x 2.5 = 1.5 inches.
(b) x 1.7 » 1.0 inches.
5. (a) The answer is about 5%
(b) New average » 65.8, new SD = 12, (80-65.8)/12 » 1.18; the answer is about 12%.
9. This looks a lot like the regression effect.
10. If the regression method were used, and you plot the "1993 predicted" against the
"1992 actual," you have to get a line--the regression line. Here, the plot is not linear. The regression method was not used to predict 1993 from 1992. (The "actual 1993"
column is not needed for the solution.)
12. True, although the difference is pretty small. The correlation is negative: the men
with 18 years of education should have blood pressures which are, on average, below
the grand average by about 2 mm (by the regression method). In other words, the men with 18 years of education should have average blood pressures of about 122 mm