A study showed that people who take St. John's Wort daily have a significantly better chance of protecting against depression than those who did not take the vitamin daily. Which of the following statements is/are correct? Can be more than one answer a. This study provides evidence that taking St. John's Wort daily contributes to protecting against depression.
b. This is an observational study and not an experiment.
c. The general health consciousness of people who take St. John's Wort could be a confounding variable.