Dr Nike Wants to Determine Whether Athletes Are Better Under

Dr. Nike wants to determine whether athletes are better under pressure than non-athletes. To study this question, Dr. Nike assigned all of the athletes to a condition in which they shoot baskets in front a group of judges. In contrast, all of the non-athletes were assigned to a condition in which they shoot baskets in a room by themselves. Dr. Nike has replicated this study multiple times with college students. What are the biggest threats to internal validity and external validity in this study