Abstract In the context of everyday reasoning, individuals inferring a causal relation between an antecedent (A) and event (E) rarely have available as evidence for their inferences frequencies of all the four possible occurences, AE, A E , A E, and AE . The present study investigated the willingness of subjects in fourth, seventh, and tenth grades, and college to infer such a relation under the more typical condition of incomplete frequency data. There was some improvement with age, but even college subjects were remarkably willing to infer a relationship based on minimal data, notably the presence of cases in the AE cell. No subjects indicated the need for information regarding the remaining cells. Subsequent presentations of datafor the A E cell did not substantially alter subjects' willingness to infer a relation, nor did subsequent presentation of data for the remaining two cells, despite the fact that complete frequency data indicated independence of A and E. A comparison group of subjects presented with all four cells at once showed somewhat more frequent application of quantitative reasoning strategies, but their willingness to infer a relationship between A and E was not notably less than that of subjects to whom the data were presented sequentially.