乡亲们
让我们来看看帕蒂在常春藤大学过得怎么样。
帕蒂在艾毅大学的教学工作已接近尾声。她不得不承认，她很舍不得这次冒险的结束。生活就是这样。
The syllabus allowed for the last few lectures to cover “Selected Topics,” so Patty decided that her selected topics would be Weibull Analysis. She felt passionately that all engineers should have some exposure to failure analysis and this topic fit right in to engineering statistics.
Before she knew it, she was heading north up to Ivy U for her next-to-the-last lecture. She thought she should soak in the beauty of the campus as her car approached, for soon this would be her last time at Ivy U for a while. Today she was lucky, she found a parking spot right away.
当她走进工程学主楼时，发现信箱里有一张纸条。是迪恩-霍华德寄来的。她迅速打开一看。他要求在她上完最后一堂课后进行一次简短的会面。
"呀！"帕蒂想，"迪安-霍华德要见我！不知道是不是真的。我是不是搞砸了？
她必须等两天才能知道院长想要什么，现在她不能担心这个，因为她的课还有 10 分钟就要开始了。
Patty 在课堂上首先解释了威布尔理论的发展，并举了几个例子。她展示了比例因子和斜率的来源。Patty 强调说，陡峭的斜率表明数据分布紧密（这对从数据中进行预测很有利），而较大的刻度则表明平均寿命较长。然后，她讨论了电子产品中不同类型测试的重要性，例如热循环测试和跌落冲击测试。作为一个例子，她认为可以分享一些电子组装中使用的两种不同合金的加速热循环数据。
她在 PowerPoint 幻灯片中展示了第一组数据（图 1）。
图 1.
"谁能给我解释一下这些结果？"帕蒂问道。
在一阵低语之后，卡伦-阿姆斯特朗举起了手。
"是的，卡伦，"帕蒂回答道。
“It appears that Alloy 2 demonstrated superior performance, as seen in its much steeper slope and slightly better scale,” Karen answered.
"干得好，凯伦，"帕蒂回应道。
“What about this one point?” Patty asked as she pointed to the obvious outlier for Alloy 1.
大家嘀嘀咕咕，但没有人举手。于是，帕蒂展示了一张去掉了离群点的幻灯片。(图 2）。
"帕蒂说："我已经删除了异常值，因为故障分析表明它是非典型的。
图 2.
“As you can see, now alloy 1 has a slightly better slope. This suggested a tighter distribution and hence more ability to predict performance,” she went on.
此时，会场上响起了非常响亮的杂音，最后斯科特-布赖津斯基举起了手。
"什么事，斯科特？"帕蒂回答道。
"斯科特解释说："教授，这看起来就像是作弊，放弃一个糟糕的数据点，因为你声称它不能代表其他样本。
许多人大声附和。
帕蒂笑了一下。
"好吧，好吧，你是对的。在大多数情况下，审查一个数据点是不公平的。这也是本课的一部分内容。不要轻易审查数据，"帕蒂说。
“Let’s look at data for Alloy 3 and 4,” Patty went on. See Figure 3.
图 3.
学生们看了一会儿数据，最后 Diane Pompey 举起了手。
"是的，黛安，"帕蒂承认道。
“They look about as dead even as one could expect, except that the sample sizes are different. Alloy 3 has 15 samples and Alloy 4 only 13 samples, as can be seen in column ‘F’ in the ‘Table of Statistics’,” Diane explained.
"帕蒂回答说："干得好，黛安，很少有人能发现这一点不同。
“I will tell you that both alloy 3 and 4 had 15 samples to start with in the test. What do you think happened?” asked Patty.
很快，弗雷德-威尔金斯举起了手。帕蒂向他点了点头。
“I’ll bet that two of the samples from alloy 4 did not fail,” Fred suggested.
"正确！"帕蒂热情地回答道。
“I want you all to take a few minutes to discuss this situation with those seated around you. I then want you to vote anonymously whether the two samples that did not fail make alloy 4 the same, better or worse than alloy 3,” Patty instructed.
After five minutes of noisy discourse, the students voted on a website, the results of which Patty could show on her laptop and project to the class. Twelve students thought the alloys were still the same. 24 thought alloy 4 was better, and 6 thought alloy 4 was worse.
"对结果有什么意见吗？"帕蒂问道。
无人问津。
帕蒂说："让我们假设这两个失效的样品经过了更长时间的测试，最终在某个很高的循环次数（比如 2000 次）上失效。让我们看看 Weibull 图会是什么样子，"帕蒂说。
然后，她展示了图 4。
图 4.
"有人能解释一下吗？"帕蒂问道。
过了没多久，Young Koh 就突袭了他的手。
“Dr. Coleman, the added cycles increased the scale significantly, but ruined the slope, suggesting much more scatter in the data. As you suggested earlier, reliability testing is about hoping to have the ability to predict lifetime. With the large decrease in the slope, prediction becomes much more difficult, So, sample 4 is likely worse than sample 3, even though it has a large scale.” Young expounded.
"正是如此，"帕蒂回答道。
“It is interesting to note that many engineers in the electronics industry today just ignore the samples that don’t fail,” Patty went on.
全班同学都一脸震惊地看着她。
"帕蒂说："好了，下次再说吧。
"两位女学生 Jessica Han 和 Mary Connor 下课后留下来与 Patty 交谈。
"教授，有传言说您下学期要教《制造工艺学》，是真的吗？"玛丽问道。玛丽接着说："我们真的希望如此。您是这里最好的老师。
帕蒂非常感动，她的眼睛开始有些迷离："谢谢你的好意，但我怀疑会不会是这样。
院长会解雇帕蒂，还是她会在下学期教授制造工艺学？敬请期待。
干杯
罗恩博士
