Which type of variance is related to a confounding variable?

Which type of variance is related to a confounding variable?

• A. Error variance (unsystematic)
• B. Error variance (systematic)
• C. Internal validity
• D. History effects

Answer: (B)

The variance tied to a confounding variable is systematic error variance. A confounder creates a consistent bias in the observed relationship between the manipulated variable and the outcome, so scores can shift in a predictable direction across groups. This kind of bias changes the average outcome in a way that isn’t due to the true effect being studied, threatening internal validity. In contrast, unsystematic (random) error adds random scatter around the true scores and doesn’t produce a consistent bias across conditions. History effects, while related to threats to internal validity, describe time-related changes rather than a specific variance type.

The variance tied to a confounding variable is systematic error variance. A confounder creates a consistent bias in the observed relationship between the manipulated variable and the outcome, so scores can shift in a predictable direction across groups. This kind of bias changes the average outcome in a way that isn’t due to the true effect being studied, threatening internal validity.

In contrast, unsystematic (random) error adds random scatter around the true scores and doesn’t produce a consistent bias across conditions. History effects, while related to threats to internal validity, describe time-related changes rather than a specific variance type.