When acting as a participant in a research study examining the relationship between alcohol consumption and driving ability, layla was assigned to the experimental group that received the highest amount of alcohol to drink. despite this ingestion of liquor, layla was still able to navigate the driver's course perfectly. the experimenter did not consider the fact that layla had been a drinker for many years, and had developed a high alcohol tolerance. this factor, which impacted the dependent variable in the study, would be called a/an variable?