Aresearcher was interested in differences in men's and women's nonverbal behavior. using a sample of 30 male and 30 female participants, he had one male and one female participant interact with one another for 20 minutes while they were videotaped. when the videotapes were analyzed, the researcher found that the nonverbal behaviors of men and women differed in many ways. identify the confound variable. (*an explanation of why it is the confound is not necessary, just identify the confound variable)