Practice Assignment (to be discussed randomly Wednesday, April 7)

1) Below are the ages of a sample of 24 couples taken from marriage licenses filed in Cumberland County, Pennsylvania in June and July of 1993. H stands for husband and W for wife.

The following scatterplot displays the relationship between husband's age and wife's age. The line drawn on the scatterplot is a 45^o line where the husband's age would equal the wife's age.

(a) Does there seem to be an association between the husband's age and the wife's age. If so, is it positive or negative? Would you characterize it as strong, moderate, or weak? Approximate the correlation coefficient.

(b) Interpret this relationship in your own words, what does it tell us about how the husband's and wife's age vary together?

(c) Summarize what one can learn about the ages of marrying couples by noting how many of the couples fall above the 45^o line, how many fall on the line, and how many fall below the line.

2) (p. 120) 2.8 3) (p. 213) 2.103

Homework Assignment (due Friday, April 9)

1) (p. 524) 7.4 (a)-(d)

2) The recent UOP election had the following results:

812 students voted, 454 voted down the initiative, 358 in favor

(a) Do these data provide significant evidence that most students were not in favor of the initiative?

(b) Any precautions we should have in interpreting these results?

3) Indicate what you would expect for the direction (positive, negative, or none at all) and strength (none, weak, moderate, or strong) or the association between the pairs of variables listed below:

(a) Height and armspan; (b) Height and shoe size; (c) Height and GPA;

(d) Latitude and avg. January temp of American cities;

(e) Cost and quality rating of peanut butter brands

(a) Construct a scatterplot to examine the relationship between a car's weight and its fuel efficiency.

(b) Describe the scatterplot (direction, form, strength, outliers)

(c) Calculate the correlation coefficient by hand. Show the details of your calculation.

(d) Circle the points corresponding to the Trucks, SUVs, and Minivans. Do you see any grouping according to this categorical variable?

(e) Calculate the regression equation for predicting the mileage from the weight of the car.

5) Many communities find a strong positive correlation between the amount of ice cream sold in a given month and the number of drownings that occur in that month. Does this mean that ice cream causes drowning? If not, can you think of an alternative explanation for the strong association? Write a few sentences addressing these questions.