Which statement best defines an extraneous variable and how it is controlled?

• A. A variable that is intentionally observed but not manipulated.
• B. An extraneous variable is any uncontrolled factor that could affect the dependent variable; controlled through randomization, standardization, and counterbalancing.
• C. A factor used to ensure consistency across trials.
• D. The primary variable of interest that is manipulated.

Answer: (B)

Extraneous variables are any factors other than the independent variable that could influence the dependent variable if they’re not kept in check. The best way to control them is by using randomization, which helps distribute unknown extraneous factors evenly across groups; standardization, which keeps procedures, environment, and instructions the same for everyone; and counterbalancing, which offsets order effects in designs where participants experience multiple conditions. These methods strengthen internal validity by preventing uncontrolled factors from biasing the results.

The statement that describes an extraneous variable as an uncontrolled factor that could affect the dependent variable and is controlled through these methods fits best. The idea of observing but not manipulating relates to a non-manipulated variable rather than an extraneous one. Describing a factor used to ensure consistency across trials points to a controlled variable, not an extraneous one. And identifying the primary variable of interest as manipulated refers to the independent variable, not an extraneous variable.