19. ABusinessWeek North American subscriber study collected data from a sample of 2861 subscribers. Fifty-nine percent of the respondents indicated an annual income of $75,000 or more, and 50% reported having an American Express credit card.

a. What is the population of interest in this study?

b. Is annual income a qualitative or quantitative variable?

c. Is ownership of an American Express card a qualitative or quantitative variable?

d. Does this study involve cross-sectional or time series data?

e. Describe any statistical inferences BusinessWeek might make on the basis of the survey.