In experimental design, which statement about extraneous variables is true?

• A. They are the main variables of interest
• B. They are intentionally manipulated
• C. They are measured after the dependent variable
• D. They are unintended factors that can influence the dependent variable

Answer: (D)

Extraneous variables are factors other than the variables you’re deliberately studying that can affect the dependent variable. They’re not the variables of interest and they aren’t intentionally manipulated. Because they’re unintended, they can influence outcomes and threaten the study’s internal validity if they differ across experimental conditions.

For example, in a study of a new teaching method, things like time of day, room temperature, or how fatigue a participant is can all act as extraneous variables. Researchers control them by random assignment, standardizing procedures, keeping conditions constant, or using control groups to ensure any observed effects are due to the method itself, not these other factors.

The other descriptions don’t fit because the essence of extraneous variables is their unintended nature and potential influence, not being the main variables, not being manipulated on purpose, and not inherently tied to the order of measurement.