A study claims that students who meditate daily score 15% higher in exams. The argument would be significantly weakened if which of the following is true?
Correct: C
Self-reliant mediation reporting via an unverified app introduces bias and measurement errors. If participants overstated their meditation time, the observed improvement may be coincidental rather than causally linked to meditation. This undermines the study’s reliability more than a non-exam period or sample size. A similar control group would maintain validity.