The original 10,000-hour rule studies relied on inconsistent retrospective recall and diaries extrapolated over a week, introducing significant noise.

“first of all no range so several of the books and the paper wrote that there was complete correspondence between the number of hours of practice and what group someone fell into and I said well I can't tell that from this data like maybe someone in the lowest group actually practiced more than someone in the highest group but you haven't included the range of practice hours or the standard deviations of practice hours”