Do Conditional Hypotheses Target Rare Events?

When testing hypotheses, rare or unexpected observations are normatively more informative than common observations, and recent studies have shown that participants' behavior reflects this principle. Research has also shown that, when asked to test conditional hypotheses ("If X, then Y") that are abstract or unfamiliar, participants overwhelmingly consider a supporting observation mentioned in the hypothesis (X&Y) to be more informative than a supporting observation not mentioned ( approximately X approximately Y). These two empirical 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 phrase conditional hypotheses in terms of rare events. Thus, observations mentioned in conditional hypotheses might generally be considered highly informative because they usually are highly informative. Copyright 2001 Academic Press.