You have decided to conduct a research study examining the relationship between depression and relationship satisfaction. To do this you have collected a sample of 12 newlywed couples. In 4 of the couples, neither partner is depressed; in 4 of the couples, one partner is depressed; in the remaining 4 couples, both partners are depressed. You plan to assess both members of each couple on relationship satisfaction and depression every 6 months for the first 5 years of marriage. What type of design is this study