1. In a 2002 study conducted on 3000 Italian 15-year-old females, girls were asked how often they consume kale each week. Four years later, these answers were linked to the girls' intelligence test scores as 19-year-olds. The study found that girls who consume kale at least once a week scored higher on the intelligence test.
2. Is this an experiment or an observational study? Explain.
3. What is the explanatory variable?
4. What is the response variable?