Which best describes a confounding variable in experimental research?

• A. It is a variable that affects only the DV
• B. It is a variable that affects only the IV
• C. It is a variable that is related to both the IV and the DV
• D. It is a variable that is unrelated to the study variables

Answer: (C)

A confounding variable is a factor that is related to both the independent variable and the dependent variable, and if not controlled, it can create a misleading impression about the relationship between those two variables. Because it ties into both the cause being studied and the outcome, it can offer an alternative explanation for any observed effect, undermining internal validity.

If a variable only affects the outcome (the dependent variable) but is not linked to the manipulation, it can change results but doesn’t explain why the manipulation would influence the outcome. If a variable only affects the manipulation (the independent variable) but not the outcome, it won’t create a spurious link between the IV and DV. And if a variable is unrelated to the study variables, it won’t produce confounding bias. The defining feature of a confounding variable is its connection to both IV and DV, which is why that description best captures the concept.