A researcher examines whether taking Vitamin D supplements (0x a day, 1x a day) influences self-reported depression (measured as either “depressed” or “not depressed”).

A. What is the independent variable?
B. What type or category of independent variable is used?
C. What is the dependent variable?
D. How many levels are there for the independent variable?
E. What is the scale of measurement for the dependent variable?