Final answer:
A confounding variable makes it difficult to determine whether an experimental outcome is due to the applied treatment.
Step-by-step explanation:
A confounding variable makes it difficult to determine whether an experimental outcome is due to the applied treatment. It is a variable that is not accounted for in the study and can influence the response variable, leading to biased results. For example, let's say a researcher is studying the effectiveness of a new drug in lowering blood pressure. If the participants in the treatment group also engage in other lifestyle changes, such as exercise or diet modifications, these additional variables can confound the results and make it unclear whether the drug alone is responsible for the observed outcomes.