For Exercise 2.1, see page 80; for Exercises 2.2 and 2.3, see page 82; and for Exercise 2.4, see page 82.
2.5 High click counts on Twitter. A study was done to identify variables that might produce high click counts on Twitter. You and nine of your friends collect data on all of your tweets for a week. You record the number of click counts, the time of day, the day of the week, the sex of the person posting the tweet, and the length of the tweet.
(a) What are the cases for this study?
(b) Classify each of the variables as categorical or quantitative.
(c) Classify each of the variables as explanatory, response, or neither. Explain your answers.
2.6 Explanatory or response? For each of the following scenarios, classify each of the pair of variables as explanatory or response or neither. Give reasons for your answers.
(a) Whether or not a person likes to sing and whether or not a person likes to dance.
(b) The number of pages in a textbook and the cost of a new copy of the textbook.
(c) The number of alcoholic drinks consumed and the blood alcohol content.
(d) In a study of adolescents, the dose of vitamin D given each day for a year (50, 100, or 200 international units) and the change in total bone mineral content from the beginning of the study to the end of the study.
2.7 Buy and sell prices of used textbooks. Think about a study designed to compare the prices of textbooks for third- and fourth-year college courses in five different majors. For the five majors, you want to examine the relationship between the difference in the price that you pay for a used textbook and the price that the seller gives back to you when you return the textbook. Describe a data set that could be used for this study, and give the key characteristics of the data.
2.8 Protein and fat. Think about a study designed to examine the relationship between protein intake and fat intake in the diets of first-year college students. Describe a data set that could be used for this study, and give the key characteristics of the data.
2.9 Soccer tickets and performance. For the teams in the Big Ten Conference last year, plan a study of the relationship between the average number of tickets sold for home soccer games and the percentage of games won. Give the key characteristics of the data that could be used for your study.