Critics point out that studies on the effectiveness of antioxidants in slowing the aging process thus far have been so-called population studies that are in nature

The answer is "correlational".

Explanation:

Antioxidants causes aging process slow, the reason behind this is that antioxidants wipe up the reactive free radicals that generally harm our DNA.  

Studies or research is correlational when there is a relationship between two variables, and we are not sure that change is one variable is due to the other.

answer; george herbert mead;

answer; lorenz;