A marketing analyst is studying the relationship between customer age groups (teens, adults, and seniors) and their preferred shopping methods (online and in-store). Which numerical measure is most appropriate for this study?

The correlation coefficient is used to measure the strength and direction of the linear relationship between two continuous variables. In this case, the variables are categorical (age groups and shopping methods), making the correlation coefficient unsuitable for analyzing the relationship in this study.

Five-number summaries, which include minimum, first quartile, median, third quartile, and maximum values, are primarily used for summarizing numerical data distributions. Since the data in this study pertains to categorical variables, five-number summaries do not apply and fail to provide relevant insights into the shopping preferences.

Mean difference is a measure used to compare the average values of numerical data between two groups. Given that the study focuses on categorical data rather than numerical data, mean difference is not applicable for determining the relationship between customer age groups and their preferred shopping methods.