AbstractThe hypothesis that people store situation and person‐by‐situation interaction information as well as trait information about one another's behavior was tested by administering modified S‐R Inventories of Anxiousness and Hostility to 54 male and 59 female undergraduates. Subjects rated the strength of affect that would be evoked by a series of situations in the two same‐sex college students whom they knew best, the best‐known opposite‐sex person, a casually known same‐sex person, and the “average college student.” Indices were constructed to measure the extent of (a) perceived average differences among people (traits), (b)perceived average differences over situations, and (c) perceived person‐by‐situation interaction. Analyses of variance showed that: (a) the ratings of the two best‐known same‐sex persons and the best‐known opposite‐sex person contained more interactive information than did the ratings of a casually known person and (b) females perceived more situational variability in the behavior of their own sex than did males. The amount of perceived person‐by‐situation interaction did not differ as a function of sex of rater or affect to be rated. It was concluded that the naive psychologist, like many professional ps