The Centers for Disease Control and Prevention noted that "the price of a pack of cigarettes went up 90% between 1997 and 2003."9 Suppose students in an introductory statistics course have been asked to identify the two variables of interest here, then tell which is explanatory and which is response, and whether each is quantitative or categorical. Which student has the correct answer? Adam: The explanatory variable is price of cigarettes, and it's categorical because it was summarized with a percentage. The response is year, and it's quantitative because it takes number values. Brittany: The roles are reversed: Year is the quantitative explanatory variable and price is the categorical response. Carlos: Year is the explanatory variable, and because just two values are possible, it's categorical. Price is the response and it's quantitative-90% just tells how much the price has changed from the year 1997 to the year 2003. Dominique: Both variables are quantitative because they both take number values; year is explanatory because it affects the price.