Gladwell's 10,000-hour rule was based on K Anders Ericsson's research on violin students' amount of practice they amassed by the time they were 20 years' old. Ericsson has since said that 10,000 was an average number, self-reported by students, and when further math and work was done, the average was closer to 7,400. Gladwell did not acknowledge that it was self-reported or an average and also guesstimated the other experts he supposed spent 10,000 hours learning something.