Answer:
A. The independent variable is the frequency of taking Vitamin D supplements (0x a day or 1x a day).
B. The independent variable is categorical.
C. The dependent variable is self-reported depression (measured as either “depressed” or “not depressed”).
D. There are two levels for the independent variable: 0x a day and 1x a day.
E. The scale of measurement for the dependent variable is nominal.