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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 …