Women are surprisingly underrepresented in the chess world, representing less that 5% of registered tournament players worldwide and only 1% of the world's grand masters. In this paper it is argued t...

the study evaluated 42 female chess players against 42 male chess players online

the organizers made the female players believe that they were playing against both female players and male players, when in reality they were always only playing against male players

as a result they saw a 50! % decrease in performance when the female players were told that they were playing against men due to gender stereotypes

keep in mind that this reduction is present not only among games with different male players, but also in games against the very same male player