“This test claims to measure mathematical ability,” Dr. Nowak says. “But it really measures how good people are at memorizing strings of numbers.” Dr. Nowak is questioning the test’s what?

Dr. Nowak is questioning whether the test actually measures mathematical ability, as it claims to. That is the test’s validity: whether it measures what it is intended to measure. The test might instead measure memorization, so the correct choice is validity.

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