Do conditional hypotheses target rare events?

When testing hypotheses, rare or unexpected observations are normatively mo re informative than common observations, and recent studies have shown that participants' behavior reflects this principle. Research has also shown th at, when asked to test conditional hypotheses ("If X, then Y") that are abs tract or unfamiliar, participants overwhelmingly consider a supporting obse rvation mentioned in the hypothesis (X&Y) to be more informative than a sup porting observation not mentioned (similar toX&similar toY). These two empi rical findings would mesh well if conditional hypotheses tend to be phrased in terms of rare, rather than common, events. Six experiments are reported indicating that people do have a tendency-often a very strong one-to phras e conditional hypotheses in terms of rare events. Thus, observations mentio ned in conditional hypotheses might generally be considered highly informat ive because they usually are highly informative. (C) 2001 Academic Press.