Which item is not typically a type of variable used in experiments?

• A. Independent variable
• B. Dependent variable
• C. Control variable
• D. Sample variable

Answer: (D)

The key idea here is how experiments identify cause-and-effect by controlling what can vary. The thing you deliberately change to see an effect is the independent variable. The thing you measure to determine the effect is the dependent variable. All other factors that could influence the outcome are kept the same or controlled so they don’t muddy the result; those are control variables. A “sample variable” isn’t a standard category because sampling deals with who is included in the study rather than a factor you actively manipulate or measure during the experiment. If there are differences among participants, those are usually described as participant or subject variables and are handled by balancing or randomizing, not treated as variables to test in the experiment. So the item that isn’t typically a type of variable used in experiments is the sample variable.