Students who voluntarily use an optional learning app obtain higher achievement scores, but they also had substantially higher prior achievement. Prior achievement is a potential:

Correct answer: confounding variable Prior achievement is related to both app use and achievement scores, so it is a potential confounding variable.

• mediator A mediator lies on the causal path between app use and achievement.
• sampling frame A sampling frame is the list from which a sample is drawn.
• dependent variable The dependent variable here is achievement, not prior achievement.