A statistics student interested in gender and grooming collects data on the shower length and gender of each person taking a shower from a random sample of showers.
A treatment center is considering changing the incentive structure for its children with Obsessive Compulsive Disorder (OCD). Two incentive systems are under consideration, Plan A and Plan B. The children at the center are randomly assigned to one of two groups. The children in the first group spend the next six months with their behavior being rewarded based on Plan A; the children in the second group are rewarded based on Plan B. Data are collected on the number of repetitive behaviors in which each child engages.
A sports psychologist is interested in the relationship between concussions and depression. He collects data from a sample of retired NFL football players, recording the number of concussions and the number of episodes of depression each experienced during his career.