A web page design firm has two designs for an online hardware store. To determine the more effective design, the firm uses one page with only teenage visitors and a second page with only adult visitors. For each visit, the firm records the amount spent by the visitor and the number of items viewed.

(a) What is the explanatory variable in this study? Is it qualitative or quantitative?

(b) What are the two response variables? For each response variable, state whether it is qualitative or quantitative.

(c) Explain how confounding might be an issue with this study.