What predicts expertise in Baduk? Intelligence, practice, and a natural test of the range restriction hypothesis.

The range restriction hypothesis suggests that intelligence-performance correlations may be underestimated in domains like chess, where most players have above-average cognitive ability. We test this hypothesis using Baduk (Go), a game of even greater complexity but, apparently, without the range restrictions in intelligence typically observed in chess. In Study 1A, experts reported significantly more serious practice alone than amateurs (d = 1.42), but scored lower in fluid intelligence (d = -1.78). In Study 1B, we invited participants back to complete a revised matrix reasoning task. We preregistered that we would observe the same finding with the new measure and, again, experts scored worse in fluid intelligence than amateurs (d = -1.79). However, this effect was no longer significant when controlling for education-suggesting that the observed intelligence gap may reflect developmental trade-offs rather than a true cognitive disadvantage among experts. Rather than fluid intelligence driving expertise, time investments in schooling versus practice appear to shape both cognitive scores and Baduk skill. (PsycInfo Database Record (c) 2026 APA, all rights reserved).