ORDER EFFECTS IN BELIEF UPDATING - THE BELIEF-ADJUSTMENT MODEL

Much literature attests to the existence of order effects in the updating of beliefs. However, under what conditions do primacy, recency, or no order effects occur? This paper presents a theory of belief updating that explicitly accounts for order-effect phenomena as arising from the interaction of information-processing strategies and task characteristics. Key task variables identified are complexity of the stimuli, length of the series of evidence items, and response mode (Step-by-Step or End-of-Sequence). A general anchoring-and-adjustment model of belief updating is proposed. This has two forms depending on whether information is processed in a Step-by-Step or End-of-Sequence manner. In addition, the model specifies that evidence can be encoded in two ways, either as a deviation relative to the size of the preceding anchor or as positive or negative vis-à-vis the hypothesis under consideration. Whereas the former (labeled estimation mode) results in data consistent with averaging models of judgment, the latter (labeled evaluation mode) implies adding models. Conditions are specified under which (a) evidence is encoded in estimation or evaluation modes and (b) use is made of the Step-by-Step or End-of-Sequence processing strategies. The theory is shown both to account for much existing data and to make novel predictions for combinations of task characteristics where current data are sparse. Some of these predictions are examined and validated in a series of five experiments. Finally, both the theory and the experimental results are discussed with respect to the structure of models of updating processes, limitations and extensions of the present work, and the importance of developing a procedural theory of judgment. © 1992.