Following the experimental design helps avoid introducing unwanted ___________ that could affect results.

• A. Measurements
• B. Levels
• C. Variables
• D. P-values

Answer: (C)

Controlling variables that could alter outcomes is essential to know whether the treatment or condition you’re testing really causes any change. Following the experimental design helps avoid introducing unwanted variables that could affect results. Extraneous or confounding variables—factors other than the independent variable that can influence the dependent variable—threaten internal validity. By sticking to standardized procedures, randomization, and consistent housing, handling, and timing, you minimize these extra influences so that differences you observe are more likely due to the factor you’re studying. Measurements are the data you collect, not something you try to prevent; different levels refer to deliberate variations of the independent variable, and p-values are statistical results, not factors introduced into the experiment.