Stat 11

February 6, 2006

Homework #3 (due Friday, February 10)

This homework is due at the start of class Friday, February 10. You may work in groups (across sections if you like), consult with others, or use any references or tools that seem useful, but you must write up your solutions yourself.

Problems from the text:

2.14 (page 119)

2.32 (page 130)

Also: In the scatterplot, show roughly where the regression line would be. Alas, correlation and regression are not useful tools in this situation.

2.55 (page 149. The formulas on p. 137 should help; there is actually more information in the problem than you need.)

2.58 (missing exams, page 149)

2.79 (confounding variables, p. 169 --- does education make you rich?)

3.6 (p. 197 – more confounding variables)

3.7 (p. 198 – still more confounding variables)

Also one more problem, modified from an earlier edition of the text:

Problem A: The Joy of Extrapolation. Here is a table showing the number of Americans living on farms, by year. (Numbers of people are in millions.)

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980

32.1 30.5 24.4 23.0 19.1 15.6 12.4 9.7 8.9 7.2

a. Using any software package, construct a scatterplot and find the least-squares

regression line. (The Excel graphics package is good enough. Or, do it

all by hand if you like.)

b. Based on the regression line, what is the predicted number of Americans

living on farms in the year 1985 ?

c. Based on the regression line, what is the predicted number of Americans

living on farms in the year 2005 ?

(end)