From the Reception section of the Wikipedia entry for Outliers
"Case Western Reserve University's assistant professor of psychology Brooke N. Macnamara and colleagues have subsequently performed a comprehensive review of 9,331 research papers about practice relating to acquiring skills. They focused specifically on 88 papers that collected and recorded data about practice times. In their paper, they note regarding the 10,000-hour rule that "This view is a frequent topic of popular-science writing" but "we conducted a meta-analysis covering all major domains in which deliberate practice has been investigated. We found that deliberate practice explained 26% of the variance in performance for games, 21% for music, 18% for sports, 4% for education, and less than 1% for professions. We conclude that deliberate practice is important, but not as important as has been argued"."
https://en.wikipedia.org/wiki/Outliers_(book)#Reception