Four experiments study relative frequency judgment and recall of sequentially presented items drawn from two categories (e.g. cities/animals). We find (a) a first-run effect whereby people overestimate the frequency of a given category when that category is the first repeated category to occur in the sequence and (b) a dissociation between judgments and memory; respondents may judge one event more likely than the other and yet recall more instances of the latter. Frequency judgements are influenced by the first run - which may reflect the operation of a judgment heuristic - while free-recall is influenced by later items
