The math SAT, for example, has limited replicability at the high end. Obtaining an 800 score usually requires making zero mistakes when answering 54 questions at a rate of one minute and 18 seconds per question. Making just three mistakes will drop a student to the 710–750 range. Consequently, it is not surprising that students who get a perfect 800 and then retake the SAT only average 752 on the retake. This is in the 97th percentile, and it is only a little higher than the 741 average achieved by students who retake the math SAT after scoring 760.
--Ashley Swanson and Glenn Ellison, Journal of Economic Perspectives, on fuzzy measurement