Measuring Strength of Evidence

在科学、法律、商业和日常社交中，人们试图将他们的信念建立在可用证据的基础上。标准的(贝叶斯)理论断言，人们的信念由各种命题的概率组成，例如，特定科学假设正确的概率或被告被指控有罪的概率。但贝叶斯理论在科学和法律上的拟议应用遇到了强烈而相当合理的抵制，很大程度上是因为该理论要求人们即使在没有任何证据(先验概率)的情况下也要表达详细的信念。这项研究将发展非贝叶斯理论，其中感知证据的强度将在数字尺度上衡量，与概率截然不同。这种测量系统很好地适应了科学和法律，因为在没有证据的情况下，所有的信念都可以被评为零。一项主要研究活动将是确定将概率和统计信息转换为证据强度衡量标准的公式，从而为这类信息与其他类型证据的系统结合提供基础。另一项研究活动将是制定统计和非统计证据的分级标准，可以根据这些标准对任意证据进行比较和评估，就像计量器提供了一系列分级的长度，可以测量其他对象的长度一样。如果证据分级标准能够被分析性地应用，将复杂的证据分解成几个部分，每一个部分都可以通过与标准进行比较来进行评估，那么分级的证据标准将是最有用的。主要的研究活动之一将是评估这种分析分解所固有的偏见。这项研究将比较两组人对部分证据的评估，其中一组人知道全部证据，另一组人不知道。如果可能，将发现这两个小组对证据的评价相同的条件，即不存在明显的偏见，因为在分析过程的任何步骤中都忽略了部分证据。这项研究还将测试预计会出现强烈偏见的条件。

In science, in the law, in business, and in everyday social interaction, people attempt to base their beliefs on the available evidence. The standard (Bayesian) theory asserts that people's beliefs consist of probabilities for various propositions, for example, the probability that a particular scientific hypothesis is correct or the probability that an accused person is guilty as charged. But proposed applications of the Bayesian theory in science and in law have encountered strong and quite justifiable resistance, largely because the theory demands that people express detailed beliefs even in the absence of any evidence (prior probabilities). This research will develop non-Bayesian theories in which perceived strength of evidence will be measured on a numerical scale quite different from probability. This measurement system is well adapted to science and the law since, in the absence of evidence, all beliefs can be rated as zero. One main research activity will be to determine formulae for converting probabilistic and statistical information to the strength-of-evidence measurement scale, and thus will provide a basis for systematic integration of such information with other kinds of evidence. Another research activity will be to develop graded standards of statistical and nonstatistical evidence, against which arbitrary items of evidence can be compared and evaluated, much as a meterstick provides a graded series of lengths, against which the lengths of other objects can be measured. The graded standards for evidence will be most useful if they can be applied analytically, decomposing a complex body of evidence into parts, each of which can be evaluated by comparison with the standards. One of the principal research activities will be to evaluate the bias inherent in such analytic decompositions. That research will compare evaluations of partial evidence by two groups of people, those who are aware of the full body of evidence and those who are not. If possible, conditions will be found for which these two groups evaluate evidence identically, i.e., there is no appreciable bias due to parts of the evidence that are ignored in any step of the analytic process. The research will also test conditions under which strong biases are expected.