Penny Gordon-Larson and her associate wanted to determine whether young couples who marry or cohabitate are more likely to gain weight than those who stay single. The researchers followed 8000 men and women for 7 years as they matured from teens to young adults. When the study began, none of the participants were married or living with a romantic partner. By the end of the study, 14% of the participants were married and 16% were living with a romantic partner. The researchers found that married or cohabiting women gained, on average, 9 pounds more than single women, and married or cohabiting men gained, on average, 6 pounds more than single men.
(a) Why is this an observational study? What type of observational study is this?
(b) What is the response variable in the study? What is the explanatory variable?
(c) Identify some potential lurking variables in this study.
(d) Can we conclude that getting married or cohabiting causes one to gain weight? Explain.