Vasta, Rosenburg, Knott, and Gaze (1997) compared the performance of four groups of male and females participants to Piaget’s water-level task, in which a participant looks at a partially full glass of water and then draws where the water level would be if the glass were tilted to the side. The four groups were bartenders, servers, clerical workers, and salespersons.

(Contrary to previous research, bartenders and servers were best. Females were generally better than males.)