Answer
This is an observational study because the individuals were free to get married or stay single (explanatory variable).
This is a cohort study.
Work Step by Step
Read the observational study definition, page 16.
This is a cohort study (page 18):
- 8000 men and women were followed (the cohort).
- They were followed for a long period of time (7 years).
- They were free of the influence of the researchers during this period.
- After this period, the weight gain was recorded (response variable).
