Type II errors. Missing something that is there. My favorite example of this is the story of Dr. Barry Marshall. I like it because it involves a hard-working scientist betting on himself and winning big and his big win has saved and improved countless lives. I also think that it is analogous to the replication crisis (which, in and of itself, seems to be highlighting instances of Type II error, eh?). Also, some correlation not equaling causation.
So, Barry Marshall. He is an Australian physician and researcher and he studies stomachs. And he had plenty of patients with stomach ulcers, and he saw first hand the suffering of his patients and death from ulcers and stomach cancer.
When Dr. Marshall was going through his medical training and the beginning of his medical career, the prevailing wisdom was that stress caused ulcers. And if you had ulcers, opportunistic bacteria called H. pylori would then prey upon the ulcer.
But this had never been proven. It was just widely accepted. But as your students should understand, correlation does not equal causation. At this point in the lecture, I ask my students to raise their hand if they experience stress. They all raise their hands. I then ask my students to raise their hands if they have a nose. I then try to argue that humans must have noses because of stress. Just because two things co-occur does not mean that one is causing the other.
Anyway, Dr. Marshall argued that the causal chain was all wrong, and that H. pylori caused ulcers, not that H. pylori was attracted to pre-existing ulcers. This is huge. The original causal understanding would dictate that you should take yoga to cure ulcers. Dr. Marshall's causal link would argue that antibiotics could successfully treat ulcers.
So he studied H. pylori. And he became increasingly convinced that the bacteria not only caused ulcers, but also stomach cancer.
Dr. Marshall wanted to test his hypothesis, but animal modeling testing was very difficult to conduct because H. pylori only live in primates (rats or mice would not do). And he didn't have those and couldn't afford those. Funding, amIrite?
Dr. Marshall couldn't get permission for human trials, either. So he decided upon a case study. He actually ingested a broth containing one of his patient's H. Pylori culture. And then he got ulcers. And then he did a bunch more research and was ignored for a long time by his peers but he kept believing in himself and eventually...won a Nobel Prize for coming up with a new course of treatment that cures ulcers and has all but eliminated stomach cancer in the Western world. I know, right?
But he was almost resigned to the file drawer. He wasn't committing the Type II error, but the rest of medicine was because they weren't paying attention to his research or taking it seriously enough.
Anyway, I really, really get into telling this story. Because it is a great story. My students love it. I think the story is engaging in general, but especially helpful as I teach many pre-PT, PA, OT, and nursing students.
Here are some articles written about Dr. Marshall, either for your own reading or maybe you could use them in class. They go into greater detail about how Dr. Marshall pieced together this mystery by carefully watching human patients who received antibiotics not for their stomach problems, but other medical issues while they happened to also have ulcers. It also highlights the role of Big Pharma and popular media picking up the story and running with it so the antibiotic cure final got the attention it deserved: