How have they proven causality? Coffee intake can be effected by other lifestyle choices. It's not unreasonable to suspect that people tend to drink coffee because they want to do perform better mentally.
For instance, a study of the cross section of the participants of this study against those who do regular mental exercise (Sudoku, balancing the checking account, playing cards) which induce caffeine intake, would be interesting.
For instance, a study of the cross section of the participants of this study against those who do regular mental exercise (Sudoku, balancing the checking account, playing cards) which induce caffeine intake, would be interesting.