I just used this example in class, and I realized that I never shared it on my blog. I really love this example of Type II error (and some other stuff, too). So here it goes.
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 correlations 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 firsthand 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 hands 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 entirely wrong and that H. pylori caused ulcers, not that H. pylori was attracted to pre-existing ulcers. This is significant. The initial understanding of causality would suggest that you should practice yoga to cure ulcers. Dr. Marshall's view, however, indicates that antibiotics could effectively 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 challenging to conduct because H. pylori only lives 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 ingested a broth containing one of his patient's H. Pylori cultures. And then he got ulcers. And then he conducted further research, which was largely ignored by his peers for a long time. Still, 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. 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, which you can read on your own or maybe use in class. They explain how Dr. Marshall uncovered this mystery by carefully observing patients who received antibiotics not for their stomach issues, but for other medical conditions. At the same time, these patients also happened to have ulcers. The articles also highlight the role of Big Pharma and the media in spreading the story, helping the antibiotic cure finally get the attention it deserved.
http://discovermagazine.com/2010/mar/07-dr-drank-broth-gave-ulcer-solved-medical-mystery
http://blogs.scientificamerican.com/guest-blog/when-scientists-experiment-on-themselves-h-pylori-and-ulcers/
https://www.nobelprize.org/nobel_prizes/medicine/laureates/2005/marshall-bio.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2661189/
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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 correlations 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 firsthand 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 hands 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 entirely wrong and that H. pylori caused ulcers, not that H. pylori was attracted to pre-existing ulcers. This is significant. The initial understanding of causality would suggest that you should practice yoga to cure ulcers. Dr. Marshall's view, however, indicates that antibiotics could effectively 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 challenging to conduct because H. pylori only lives 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 ingested a broth containing one of his patient's H. Pylori cultures. And then he got ulcers. And then he conducted further research, which was largely ignored by his peers for a long time. Still, 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. 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, which you can read on your own or maybe use in class. They explain how Dr. Marshall uncovered this mystery by carefully observing patients who received antibiotics not for their stomach issues, but for other medical conditions. At the same time, these patients also happened to have ulcers. The articles also highlight the role of Big Pharma and the media in spreading the story, helping the antibiotic cure finally get the attention it deserved.
http://discovermagazine.com/2010/mar/07-dr-drank-broth-gave-ulcer-solved-medical-mystery
http://blogs.scientificamerican.com/guest-blog/when-scientists-experiment-on-themselves-h-pylori-and-ulcers/
https://www.nobelprize.org/nobel_prizes/medicine/laureates/2005/marshall-bio.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2661189/
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