Thanks for writing this up! It’s definitely given me a lot to think about. My model of the doctors’ minds falls into two real reasons:
1. If you choose not to order a biopsy, or the like, because of base rate estimates, you are incurring a lot of risk. Even if you are entirely correct that it is low risk, I would very much expect that if you follow that pattern for long enough, you will have at least one patient for whom it is actually cancerous, and my understanding is that you could very easily be sued for malpractice in that case.
2. If you know the biopsy is going to be not worth running, or at least “know” to a good probability, before you even do the initial test, you really are wasting money running that test!
Oh my God. I just had this fight with an MD and NP. An old woman suddenly gets demented. Well, urinary tract infections can cause that. Oh, but we can't test old ladies for UTIs because turns out old ladies often have bacteria in their urine that isn't causing any harm. So then we overtreat old ladies, and overtreating is way worse, apparently, than treating the subset of old ladies who could be brought back out of dementia by getting their UTIs treated. My late mother tended to get demented with UTIs and get better after treatment, so I'm cranky about this trend. I'll probably get them too and no one will test and treat and I'll die demented because OTHER old ladies have asymptomatic bacteriuria.
Thank you for writing about this! I've also been very frustrated to hear about it.
I suspect it's largely explained by medical liability. If you're a doctor and you estimate that a weird nodule is probably not worth the painful and risky biopsy, you gain nothing when it's actually nothing, but you'll be sued for ignoring it in the cases where it turns out to be a problem. Scott Alexander has a post about the stories doctors tell each other about this kind of thing (he flags at the top of the post that this particular story is fishy, but that doesn't affect that doctors believe that this kind of thing happens): https://slatestarcodex.com/2014/06/23/court-ing-disaster/
This article, Overtreatment in the United States, describes a survey of doctors from the AMA, and notes that "At 85% of respondents, “fear of malpractice” was the top cited reason for overtreatment."
I feel I'm being foolish: I think the problem is that Big Eddie isn't a liar. And so we could be in a situation where it is rationnal for any given individual to do something that still shouldn't be done by the group of these individuals.
First, it could be that the test (CT scan, blood test...) was only studied among high risk people, which would make non obvious whether we could apply the same sensibility and specificity among low risk people.
Assuming it is the case, the risk of the biopsy would be, hopefully, fairly low. And both in high risk (obviously) and low risk people, the Positive Predictive Value could be fairly high considering the disease tested for. So in both case, one should opt for the biopsy when tested positive.
Yet, testing low risk people on a daily basis, *because* they would rationnaly opt for the biopsy when tested positive, would end up generating *in the population of low risk people* far more iatrogenic complications, undue psychological distress etc.. than would be rationnaly justified by the prevalence of the disease in this (very) huge group.
The obvious thing missing from your beautiful utility calculations is that besides the risks for the patient, there are also risks for the doctor; legal risks, reputational risks, etc., etc. Include them, and everything makes perfect sense (except American medicine itself, of course).
Thanks for writing this up! It’s definitely given me a lot to think about. My model of the doctors’ minds falls into two real reasons:
1. If you choose not to order a biopsy, or the like, because of base rate estimates, you are incurring a lot of risk. Even if you are entirely correct that it is low risk, I would very much expect that if you follow that pattern for long enough, you will have at least one patient for whom it is actually cancerous, and my understanding is that you could very easily be sued for malpractice in that case.
2. If you know the biopsy is going to be not worth running, or at least “know” to a good probability, before you even do the initial test, you really are wasting money running that test!
Regardless, very much appreciate the post!
Oh my God. I just had this fight with an MD and NP. An old woman suddenly gets demented. Well, urinary tract infections can cause that. Oh, but we can't test old ladies for UTIs because turns out old ladies often have bacteria in their urine that isn't causing any harm. So then we overtreat old ladies, and overtreating is way worse, apparently, than treating the subset of old ladies who could be brought back out of dementia by getting their UTIs treated. My late mother tended to get demented with UTIs and get better after treatment, so I'm cranky about this trend. I'll probably get them too and no one will test and treat and I'll die demented because OTHER old ladies have asymptomatic bacteriuria.
Thank you for writing about this! I've also been very frustrated to hear about it.
I suspect it's largely explained by medical liability. If you're a doctor and you estimate that a weird nodule is probably not worth the painful and risky biopsy, you gain nothing when it's actually nothing, but you'll be sued for ignoring it in the cases where it turns out to be a problem. Scott Alexander has a post about the stories doctors tell each other about this kind of thing (he flags at the top of the post that this particular story is fishy, but that doesn't affect that doctors believe that this kind of thing happens): https://slatestarcodex.com/2014/06/23/court-ing-disaster/
This article, Overtreatment in the United States, describes a survey of doctors from the AMA, and notes that "At 85% of respondents, “fear of malpractice” was the top cited reason for overtreatment."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5587107/
I feel I'm being foolish: I think the problem is that Big Eddie isn't a liar. And so we could be in a situation where it is rationnal for any given individual to do something that still shouldn't be done by the group of these individuals.
First, it could be that the test (CT scan, blood test...) was only studied among high risk people, which would make non obvious whether we could apply the same sensibility and specificity among low risk people.
Assuming it is the case, the risk of the biopsy would be, hopefully, fairly low. And both in high risk (obviously) and low risk people, the Positive Predictive Value could be fairly high considering the disease tested for. So in both case, one should opt for the biopsy when tested positive.
Yet, testing low risk people on a daily basis, *because* they would rationnaly opt for the biopsy when tested positive, would end up generating *in the population of low risk people* far more iatrogenic complications, undue psychological distress etc.. than would be rationnaly justified by the prevalence of the disease in this (very) huge group.
The obvious thing missing from your beautiful utility calculations is that besides the risks for the patient, there are also risks for the doctor; legal risks, reputational risks, etc., etc. Include them, and everything makes perfect sense (except American medicine itself, of course).