Which of the following correctly defines a confounding variable?

A confounding variable is best described as a variable that affects the outcome but is not controlled. In experimental research, confounding variables introduce ambiguity because they can be related to both the independent variable (the factor being manipulated) and the dependent variable (the outcome being measured). This means that if a confounding variable is not accounted for, it can lead to incorrect conclusions about the relationship between the independent and dependent variables. For instance, if researchers are studying the effect of a new medication on blood pressure but fail to control for age as a confounding variable, age could influence blood pressure independently of the medication, leading to misleading results.

Understanding confounding variables is crucial in research design because controlling for them helps isolate the effect of the independent variable on the dependent variable, leading to clearer and more reliable findings.