a study found an association between preferred warm beverage and stress level. it showed tea drinkers have lower stress levels than coffee drinkers. tea drinkers are known to have a higher proportion of yoga practitioners than coffee drinkers, and they exercise on average two hours per week more than their coffee-drinking counterparts. what is the term used to describe these additional factors that might have an effect on the stress levels of tea drinkers? responses categorical variables categorical variables cause-and-effect variables cause-and-effect variables confounding variables confounding variables quantitative variables quantitative variables response variables