A recent Harvard study concluded that people who drink coffee tend to live longer than those who don't drink coffee. The study followed more
than 20,000 nurses and doctors over a 30-year period, giving them
frequent questionnaires to answer about their coffee habits. Researchers
found that people who drank 3 to 5 cups of coffee a day had a mortality
rate during the study that is 15% lower than those who did not drink
What is the explanatory and response variable and what kind of study is it