Dr. Peiffer recently conducted a study on marital satisfaction. After surveying 100 married couples, she found that couples who commit to a date night once a week report higher marital satisfaction than those who do not date weekly. She was unsure whether the dates contributed to marital satisfaction, or if happy couples were more likely to date. To further investigate her findings, she asked 50 unhappy couples to date once a week. After 12 weeks, she found that all of the couples reported an increase in marital satisfaction. What term describes Dr. Peiffer’s findings?