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This experiment examined the role that ambiguity and uncertainty play in the use of base rate and individuating information in probability judgments. Subjects responded to a number of inference problems that varied in terms of base rates and the accuracy of the source of the individuating information. The ambiguity in the decision situation was also manipulated by varying the human or technological nature of the source of the individuating information and the causal relevance of the base rate information. The results provide substantial support for the predictions derived from the ambiguity conceptualization. Several interactions were uncovered involving attributes of the base rate and individuating information suggesting complex judgmental processes similar to anchoring and adjustment. Discussion focused on the role that human versus technological sources of information may play in judgment and decision making, and the utility of the ambiguity notion for understanding the use of base rate and individuating information in probabilistic inference problems.