If the measurement device changes during the course of a within-subjects study so that the participants' scores are influenced, internal validity is threatened by statistical regression.

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Quizplus · Accepted Answer

The threat described is instrumentation, not statistical regression. Instrumentation refers to changes in the measurement device or procedure that can affect the outcomes, whereas statistical regression involves extreme scores moving towards the mean over time.

If the Measurement Device Changes During the Course of a Within-Subjects