
How Well Do We Understand Probabilities in Medicine? (2016) - bladecatcher
https://psychscenehub.com/psychinsights/well-understand-probabilities-medicine/
======
rcdmd
Reading some comments in this thread you might think physicians are unable to
apply Bayesian statistics to medical care. As a physician myself, I'd
encourage a more considered line of thinking.

Clearly, physicians here failed to calculate an exact positive predictive
value in the example. The question is does that inability affect their 1)
medical care delivered and 2) communication with the patient and the patient's
own informed decision-making.

In speaking to 1-- there are many examples to choose from from probably any
medical specialty but let's stick to breast cancer screening since that's the
example from the article. USPSTF presents their recommendations[1]. I'd
encourage anyone with interest to at least skim the rationale presented on the
page below those recommendations. They very well consider prevalence as well
as efficacy of specific tests given the presence of different risk factors in
a patient (age, family history, etc). Importantly, those and many other
screening guidelines are applied by primary care physicians who may not
otherwise be able to calculate exacting probabilities.

[1]
[https://www.uspreventiveservicestaskforce.org/Page/Document/...](https://www.uspreventiveservicestaskforce.org/Page/Document/RecommendationStatementFinal/breast-
cancer-screening1)

In speaking to 2-- patient autonomy of course requires an appropriate
understanding of the tests they receive, any risk to those tests and the
benefits and harms of true positives, false negatives, etc. The associated
frequencies, albeit with some degree of imprecision are avaialble by reference
and I'd suspect they're memorized by most radiologists reading mammograms and
the breast surgeons involved in tested positives-- even if they may not be
able to calculate them. If the doctor doesn't have them memorized-- they
should be available by referencing the relevant guideline.

~~~
User23
I've never once in my life been able to give real informed consent to a
physician, because I've never had one able to inform me quantitatively of the
risks and benefits of accepting or refusing treatment. So like, I assume,
everyone else I pretty much just have to take what the doctor says on blind
faith. Since the vast majority of physicians are good people who actually want
to help their patients, I'm not entirely uncomfortable with this, but it's
still troubling given how many people die every year as a result of
interventions or complications thereof.

~~~
rcdmd
I too wish everything in medicine was cut and dry. But oftentimes precise
numbers are unavailable. More qualitative reasoning such as "high risk,"
"serious morbidity or mortality" is usually given in medical assessments.
Plans are developed based off that assessment. Doctors and patients routinely
make well-considered decisions and get consent knowing that exact numbers
aren't known. On the other hand, many treatments (pharmaceuticals and
screening being 2 major ones) are backed by very reliable studies where
numbers are known.

~~~
Nomentatus
Yet the point is that even when the numbers are absolutely clear cut and are
more than relevant to medical decision making, doctors' training doesn't help
them reason their way out of a wet paper bag. They're hopeless even when
they're provided with a problem that has the equivalent of training wheels and
handrails.

------
iheartpotatoes
BSEE and MSEE with 8 years of heavy math and the fact that I still have to
read the solution slowly and not really get it scares the bejeezers out of me.

~~~
tnecniv
This is a little surprising to me. I was required to take a probability class
for my BS in electrical engineering, and a version of this problem was a
homework question.

~~~
iheartpotatoes
Funny you should call this out: As an undergrad I got to choose between a prob
& statistics path and a complex math / advance calc path. I took the complex
math path. However, I was required to take a semester on engineering methods
that touched on statistics, but that was part of one semester. As a grad
student, I went down the numerical methods path for parallel computing. Not as
many classes as undergrad, but still.

College: RPI. Graduation year: '91.

------
DanBC
Bit annoying that this article hat-tips Taleb, when Gerd Gigerenzer has been
doing this better and for longer.

This book is a good introduction, includes a lot of anecdote from different
health care professionals across a range of different testing (including
cancer and HIV), and mentions the research across different health care
professionals.

[https://www.amazon.com/Reckoning-Risk-Learning-Live-
Uncertai...](https://www.amazon.com/Reckoning-Risk-Learning-Live-
Uncertainty/dp/0140297863/)

Here's an extract: [https://imgur.com/zO4zkl4](https://imgur.com/zO4zkl4)

------
fred_and_fred
This topic comes up here periodically, and I've linked to these articles
before, but it's probably worth doing so again for those interested. I am a
physician who was also puzzled by these matters, and wound up inventing a
simple diagram that I use as a mental "widget" to manipulate the ideas of the
2x2 table in my head. The full text articles can be found at:
[https://www.researchgate.net/profile/Kevin_Johnson40](https://www.researchgate.net/profile/Kevin_Johnson40)

P.S. I'd love to have someone animate this in Javascript!

~~~
fred_and_fred
The code for an R version of this is on Github at [https://github.com/two-by-
two](https://github.com/two-by-two)

There is a limited demo there as well.

------
mrnobody_67
I always wonder the pros/cons of getting tested for no specific symptom...
anxiety.stress.costs of false positives could be enormous.

There's even a book & several articles out there arguing that getting tested
for cancer might be a bad idea:
[https://www.theatlantic.com/health/archive/2015/06/should-I-...](https://www.theatlantic.com/health/archive/2015/06/should-
I-get-tested-screened-for-cancer/397100/)

------
known
Science, Statistics and Lies
[https://en.wikipedia.org/wiki/Lies,_damned_lies,_and_statist...](https://en.wikipedia.org/wiki/Lies,_damned_lies,_and_statistics)

------
progval
Sadly unsurprising. I remember reading a conversation on Twitter where a
psychologist wrote openly "I don't use statistics because I have an analytical
orientation".

------
tcj_phx
I find it ironic that this article is posted on a website aimed at the mental
health industry. The actual challenge faced by mental health practitioners is
with the futility of their approach.

I met a young man (early 20's) who'd recently arrived in town for the purposes
of "recovery". Having learned something about people's problems with self-
medicating I asked, "People usually know when their problems with substances
started. When did it start for you?"

He instantly said that when he was in third grade his teacher thought he was
disruptive. Parents took him to the doctor, who prescribed medication. When he
got to 9th grade he gave his parents an ultimatum: "if you don't take me off
these drugs, _I 'm going to kill myself._" His parents promptly took him off
the drugs that didn't address the boredom he'd experienced in his suffocating
3rd grade classroom, and that's when he started self-medicating with whatever
he could get his hands on.

The DSM is the mental health industry's guide to help practitioners precisely
diagnose symptoms. The problem is the industry frequently jumps to treatment
without concern as to the cause of the patients' symptoms.

Court-ordered treatment (aka "assisted outpatient treatment") is where the
mental health industry decides to force a patient to take the drugs they think
they need. I have the affidavits that were filed against my friend. They say,
essentially, "Patient expects us to believe that her symptoms are related to
consuming 2 bottles of liquor a day. She is clearly in need of court-ordered
treatment because she does not believe that she has a chronic condition. We
know that she has a chronic condition because she's had two previous orders
for treatment. She took herself off our forced services 4 years ago, and here
she is again."

Before this went down, I'd decided that my friend's substance abuse problems
were related to her having been adopted, exposed to meth amphetamine as a pre-
teen, having "lost her future" at 16 years old when she was expelled for self-
medicating with what is now approved as a breakthrough therapy for PTSD
(MDMA), and having been injected with a prescription endocrine disruptor [0]
with the black-box warning of "cortisol deficiency" at 18 or 19 years old.
This "birth control" drug is known to make some women suicidally-depressed.
Cortisol deficiency is now associated with psychosis. My friend allowed that
maybe the injections took her from "drug abuser" to "drug addict".

[0] [https://en.wikipedia.org/wiki/Depo-
Provera](https://en.wikipedia.org/wiki/Depo-Provera)

In the world where mental health professionals address causes rather than
symptoms and treat conservatively when the causes of a condition are unknown,
those doctors would have recognized my friend's presentation as a form of
substance-induced psychosis [1], and provided support to help her sober up.

[1] [https://en.wikipedia.org/wiki/Substance-
induced_psychosis](https://en.wikipedia.org/wiki/Substance-induced_psychosis)

Rather than provide rational treatment, they just force her to take "anti-
psychotics" in the delusional belief that their drugs (rather than sobriety)
are what allows my friend to be functional. At one point they thought she
needed two different drugs. My friend explained her presentation as, "I'm
sorry, these drugs make us slow".

Every medical specialty has practices that aren't actually justified by the
findings of science. I believe Psychiatry is the most important of the medical
specialties, but the path "mainstream" practitioners has taken since the
1950's has been a mistake: most psychiatric drugs are just modern FDA-approved
"patent medicines" [2] that don't actually address the causes of the patient's
symptoms. While some people like their psych drugs, they'd probably do much
better with more scientific approach to their complaints.

[2]
[https://en.wikipedia.org/wiki/Patent_medicine](https://en.wikipedia.org/wiki/Patent_medicine)

~~~
CWSZ
_Rather than provide rational treatment, they just force her to take "anti-
psychotics" in the delusional belief that their drugs (rather than sobriety)
are what allows my friend to be functional._

My best friend's father is a paranoid schizophrenic. Antipsychotic medication
allows him to live a relatively normal life.

~~~
tcj_phx
> My best friend's father is a paranoid schizophrenic. Antipsychotic
> medication allows him to live a relatively normal life.

How do you know that it's the medication that allows him to "live a relatively
normal life", and not the other factors?

If you want to trade anecdotes... My other friend's father fell out of a tree
and broke his back when she was a child (iirc). Some time later they decided
he was a "schizophrenic". He's been on antipsychotics ever since. His
condition has spiraled downward over the subsequent years. Last I heard he was
full-on crazy. If the doctors had provided supportive treatment instead of
suppressive, his life trajectory would have been totally different.

My aunt's good friend had a "psychotic break" soon after her husband died
unexpectedly. The friend was put on "anti-psychotics". She's now dying of
liver failure, certainly as a consequence of her long-term drugging.

The ugly truth about so-called "antipsychotic medication" is that the class is
palliative rather than curative, and actually causes the deterioration it
supposedly treats.

Robert Whitaker makes the case that medications turns people's "episodes" into
chronic conditions: [https://www.madinamerica.com/2016/07/the-case-against-
antips...](https://www.madinamerica.com/2016/07/the-case-against-
antipsychotics/) and [https://www.madinamerica.com/2018/03/a-tale-of-two-
studies/](https://www.madinamerica.com/2018/03/a-tale-of-two-studies/) and
[https://www.madinamerica.com/2017/09/thou-shall-not-
criticiz...](https://www.madinamerica.com/2017/09/thou-shall-not-criticize-
our-drugs/) , for example.

~~~
CWSZ
I dislike exchanging anecdotes too. If you can point me to a treatment for
schizophrenia tested in quality randomized trials with the success rate of
antipsychotics (which still have a very poor success rate), please do.

~~~
tcj_phx
_Mad in America_ makes reference to an approach to psychosis from Finland
called "open dialogue".
[http://psychrights.org/Research/Digest/Effective/OpenDialogu...](http://psychrights.org/Research/Digest/Effective/OpenDialogue2yfollowupehss0204.pdf)

It was recently re-established that psychosis is linked to cortisol
deficiency: [https://psychcentral.com/news/2016/06/04/low-morning-
cortiso...](https://psychcentral.com/news/2016/06/04/low-morning-cortisol-
levels-linked-to-psychosis/104266.html) \- the first such linkage was in the
1950's, but this observation was never put to mainstream use.

Psychosis is fundamentally a condition of metabolic stress. Vitamin B-3
(niacin/niacinamide) was found to help patients recover:
[https://riordanclinic.org/2014/11/niacin-and-
schizophrenia-h...](https://riordanclinic.org/2014/11/niacin-and-
schizophrenia-history-and-opportunity/)
[http://orthomolecular.org/resources/omns/v13n23.shtml](http://orthomolecular.org/resources/omns/v13n23.shtml)
[http://orthomolecular.org/resources/omns/v10n18.shtml](http://orthomolecular.org/resources/omns/v10n18.shtml)

> If you can point me to a treatment for schizophrenia tested in quality
> randomized trials with the success rate of antipsychotics (which is really
> miserable), please do.

It will be 15-20 years for a randomized trial initiated today to get such a
result. Who would pay for such studies? The businesses who've been making
$billions on their FDA-approved drugs for decades? The status quo defends
itself, and refuses to admit they made a mistake in forcing palliative
treatments on vulnerable patients.

~~~
killjoywashere
As I'm sure you're aware, there's a thing called the Dunning-Kruger effect,
which predicts that people with less knowledge are more confident in their
grasp of the situation than people who really do know what's going on. Reading
your comments makes me wonder if perhaps you might want to reflect on whether
you've seen 10,000 psychiatric patients on the in-patient wards. If not, I'm
guessing you may want to revisit the possibility that the thousands of
psychiatrists and nurses on the floors, who have invested their lives in
caring for the sick might have a better appreciation for the signal-to-noise
ratios that matter in the present topic of discussion.

It seems you consider yourself wise. If that's true, I suspect you will
recognize the value of at least projecting humility in the face of the
cummulative lifetimes of effort others have invested in a problem.

~~~
tcj_phx
The opposite side of Dunning-Kruger's coin is that "competent students tended
to underestimate their own competence" [0]. I have no idea where I fall on the
spectrum, I just try to be observant. I read books, and check references when
it seems important. The science library at the nearest State University is
quite useful for this purpose. I'm working on a model to help me understand
what's going on. There are lots of holes in my model, and I'd certainly take
myself straight to the hospital if I sustained a sudden injury (broken bone,
etc).

[0]
[https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect#...](https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect#Later_studies)

I have videos from 2 weeks before my friend ran out of alcohol that show she
was not psychotic when on her maintenance dose of alcohol. She was with me the
weekend her mother said she "disappeared" \-- I'd encouraged her to call her
mother, but she did not do so. She ran out of alcohol when I took her home.
She called me the next morning. I knew something was happening, but I didn't
know anything about "psychosis" at the time. If I'd known then what I now know
about withdrawal psychosis, I'd have called her mother right away...

I have the affidavits from the hospital's application for court-ordered
evaluation, and the psychiatrists' affidavits from her first prosecution for
having a "persistent or acute disability" (ambiguity in statute), even though
the statutes distinguish between "mental disorders" and conditions resulting
from "drug abuse, alcoholism or intellectual disability." I witnessed her
deterioration while getting the finest of the mental health industry's
standard of care. I drove five hours to retrieve my friend the day after she
was released from a "stabilization" that left her more delusional at the end
of the week than at the beginning.

There is a resistance against conventional psychiatry because of the field's
long history of harmful treatment: Lobotomies, water torture, palliative
medications, [edit: electrocution], etc. Robert Whitaker examined the
predicament of the "mentally ill" in his first book, _Mad in America_ :
[https://books.google.com/books?isbn=0786723793](https://books.google.com/books?isbn=0786723793)

The tragedy of the situation is that the Quakers figured out how to
compassionately care for people while they had mental episodes (Ref:
Whitaker's book). This was without the benefit of the sciences' contributions
to humanity's understanding of our condition. Furthermore, 20th Century
Science figured out the physiological considerations behind most so-called
"mental" conditions. For some reason, psychiatry didn't incorporate these
findings into clinical practice. Whitaker makes the case that psychiatry has
been compromised by profiteers in the drug industry in his third book,
_Psychiatry Under the Influence_ :
[https://books.google.com/books?isbn=113751602X](https://books.google.com/books?isbn=113751602X)

People have rights, even people who are declared to have a "mental disorder",
but most such patients have trouble asserting their rights on their own. I had
a breakthrough last month, and am now confident that my last 3 years of
efforts have not been in vain.

Thank you for reminding me of the importance of humility.

