WileyPLUS Adaptive Practice Statistics: Unlocking the Power of D... Ch 1: Collecting Data (18 of 19) Q 1.18: An observational study revealed that respondents between 30 and 40 years old own more cars on average tha the respondents between 20 and 30 years old do. What are the possible confounding variables (if any) in this association? Select all that apply. A The older respondents have families more often, so they need to provide the transportation for it. B The professional skills of the respondents grow, as they work, so they are paid more, and are able to own a car (or several). People over 20 years periodically buy a new car, so they own more of them after a longer period of time