Traditionally, the risk priority number (RPN) is used to compute the failure risk by multiplying occurrence, detection, and severity factors. Claiming that the key feature of multiplying the three factors together to get the RPN is a limitation of this method, existing studies have developed the multiple criteria decision making (MCDM) approach. In this paper, we first show that the multiplication of the three factors is indeed useful not only for evaluating the failure risk based on the trade-off between the improvement cost and risk reduction but also for identifying an appropriate action to reduce the risk of a fixed failure only if failure data is available for evaluating each of the three factors. We then develop a modified method to use the well-established multiplication operation even when each factor is evaluated by an expert. A numerical example is presented to illustrate the advantage of the modified method over the previous MCDM approach in determining the effectiveness of action plans for system risk reduction when only qualitative data is available.

传统上，风险优先级数字（RPN）用于通过将发生，检测和严重性因子相乘来计算故障风险。声称将三个因素相乘以获得RPN的关键特征是该方法的局限性，现有研究已经开发了多标准决策方法（MCDM）。在本文中，我们首先表明，这三个因素的乘积确实不仅对基于改进成本和降低风险之间的权衡评估失败风险很有用，而且对于确定降低风险的适当措施也非常有用。仅当故障数据可用于评估三个因素中的每个因素时，才修复故障。然后，我们开发了一种改进的方法，即使每个因素都由专家评估，也可以使用公认的乘法运算。