Probability information is regularly communicated to experts who must fuse multiple estimates to support decision making. Such information is often communicated verbally (e.g., “likely”) rather than with precise numeric (point) values (e.g., “.75”), yet people are not taught to perform arithmetic on verbal probabilities. We hypothesized that the accuracy and logical coherence of averaging and multiplying probabilities will be poorer when individuals receive probability information in verbal rather than numerical point format. In four experiments (N = 213, 201, 26, and 343, respectively), we manipulated probability communication format between subjects. Participants averaged and multiplied sets of four probabilities. Across experiments, arithmetic accuracy and coherence was significantly better with point than with verbal probabilities. These findings generalized between expert (intelligence analysts) and non-expert samples and when controlling for calculator use. Experiment 4 revealed an important qualification: Whereas accuracy and coherence were better among participants presented with point probabilities than with verbal probabilities, imprecise numeric-probability ranges (e.g., “.70 to .80”) afforded no computational advantage over verbal probabilities. Experiment 4 also revealed that the advantage of the point over the verbal format is partially mediated by strategy use. Participants presented with point estimates are more likely to use mental computation than guesswork, and mental computation was found to be associated with better accuracy. Our findings suggest that where computation is important, probability information should be communicated to end users with precise numeric probabilities.

中文翻译：

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概率词和数字的算术计算

概率信息定期传达给专家，他们必须融合多个估计以支持决策。此类信息通常通过口头（例如，“可能”）而不是精确的数字（点）值（例如，“.75”）来传达，但人们并未被教导对口头概率进行算术运算。我们假设当个人以口头而不是数字点格式接收概率信息时，平均和相乘概率的准确性和逻辑一致性会更差。在四个实验中（N = 213、201、26 和 343），我们操纵了受试者之间的概率通信格式。参与者平均并乘以四个概率的集合。在整个实验中，点的算术准确性和连贯性明显优于口头概率。这些发现在专家（情报分析师）和非专家样本之间以及在控制计算器使用时得到了概括。实验 4 揭示了一个重要的条件：虽然用点概率呈现的参与者的准确性和连贯性比用语言概率呈现的要好，但不精确数字概率范围（例如，“.70 到 .80”）比口头概率没有计算优势。实验 4 还表明，点相对于口头格式的优势部分是由策略使用所介导的。接受点估计的参与者更有可能使用心理计算而不是猜测，并且发现心理计算与更高的准确性相关。我们的研究结果表明，在计算很重要的地方，应该将概率信息以精确的数字概率传达给最终用户。