ABSTRACT
Hindsight bias and anchoring effects are demonstrated in studies in which participants have to answer difficult questions (for an overview see Hawkins & Hastie, 1990). Typically, these questions are designed in such a way that only a few participants know the correct answer. Participants are therefore forced to generate uncertain estimates. A characteristic of this kind of cognitive task is that the obtained estimates may be systematically biased if specific information is provided to the participants before they estimate. Participants are usually not aware of this manipulation (Fischhoff, 1975) and there are obviously only a few situations where hindsight bias or anchoring effects are considerably reduced or eliminated (Erdfelder & Buchner, 1998, Exp. 3; Hasher, Attig, & Alba, 1981; Pohl, 1998). Hindsight bias and anchoring effects are studied with slightly different procedures. Two experimental designs are commonly used to study hindsight bias (Fischhoff, 1977). One is the “hypothetical design”, in which the solution to the question is presented right at the beginning of the experiment. Participants are then asked to make an estimate without considering the given solution, that is, “as if they didn’t know the correct answer”. Compared to control items (for which the solution was not presented), the estimates for the experimental items are biased towards the given solution. In the case of a “memory design”,
participants first make an estimate. After a retention interval (usually a few days), the solution is presented before they are finally asked to remember their previous estimate. This design, too, reveals a systematic bias of the estimate towards the given solution. Thus, in both designs, hindsight bias (or the “knew-it-all-along-effect”, Wood, 1978) consists of a shift of generated or remembered estimates towards the previously presented solution. In a meta-analysis covering 128 studies, ChristensenSzalanski and Willham (1991) found only six studies in which no hindsight bias was revealed. This effect thus seems to be extremely robust (Pohl & Hell, 1996).
