posted by please help .
Will taking antioxidants help prevent colon cancer?
A medical experiment divided subjects into four gruops:daily beta-carotene, daily vitamins C and E, all three vitamins every day or daily placebo to determine if they help prevent colon cancer.
1. What are the explanatory and response variables in this experiment?
My question: Is the placebo considered an explanatory variable??
I know the beta-carotene, vitaminds C and E, and all three vitamins are. The response variable is the incidence of cancer.