I recently listened to the episode ‘What’s Wrong with the IAT? (with Jesse Singal)’ of the podcast ‘Two Psychologists Four Beers’ (https://fourbeers.fireside.fm/13). The hosts together with their guest Jessy Singal discuss the IAT (a psychometric test). At around 38:35 min, Jessy explains that the test only explains about 1% of the variance in behavioral outcomes and concludes, together with the hosts, that the test does not predict behavior on the individual level but only on the aggregate level (i.e. on population level).
I wonder what that means, ‘not predictive on the individual level but on the aggegrate level’ (or on average?). Is this a property of a test? Is there a cut off value for this? Is this simply another way of saying the effect size is extremely small?