In experiments, does the Control group form part of the independent variable?

Lets say there's an experiment consisting of two groups, a group of Depressed subjects and a control group of Non-Depressed subjects.. with certain drug treatments to be tested on them and measurements taken.



Would one of the independent variables be Depressed/Non-Depressed? Or does information about the control group not form part of the independent variable?In experiments, does the Control group form part of the independent variable?
Yes, the control group (and the experimental group) do constitute an independent variable. An independent variable is basically any differences in your sample that you explicitly manipulate (by assigning people to conditions) and/or make comparisons between.



So in the case you describe, a simple design would be



Depressed vs non-depressed, where you have 1 IV.



If you're varying the types of treatment used, you could have 2 IVs, being



IV1 = depressed vs non-depressed

IV2 = Drug type a vs drug type b vs placebo (placebos are often used as controls in drug trials)



Similarly a 3 IV design might be:



IV1 = depressed vs non-depressed

IV2 = Drug type

IV3 = Male vs female



An independent variable refers to the dimension on which they differ (e.g. their depression status, their sex status etc.), rather than what the groups you separate them into are within that (be it 2 groups, 5 groups etc.).