Can you outsmart the fallacy that fooled a generation of doctors? - Elizabeth Cox

Oh the humanity!

Ah...humanity...

It’s a trainwreck,
but I can’t look away.

It’s 1843, and a debate is raging
among physicians

about one of the most common
killers of women: childbed fever.

Childbed fever strikes within days of
giving birth,

killing more than 70% of those infected—
and nobody knows what causes it.

Obstetrician Charles Meigs has a theory.

Having observed abdominal inflammation in
patients who go on to develop the fever,

he claims this inflammation is the cause
of childbed fever.

Much of the medical establishment
supports his theory.

Oh, come on!

They really leave me no choice but
to teach them some skepticism.

That’s better.

Now, Meigs, your argument is based
on a fallacy—the false cause fallacy.

Correlation does not imply causation:

When two phenomena regularly occur
together,

one does not necessarily
cause the other.

So you say women who have inflammation
also come down with childbed fever,

therefore the inflammation
caused the fever.

But that’s not necessarily true.

Yes, yes, the inflammation comes first,
then the fever,

so it seems like the inflammation
causes the fever.

But by that logic, since babies usually
grow hair before teeth,

hair growth must cause tooth growth.

And we all know that’s not true,
right?

Actually, don’t answer that.

A couple of different things
could be going on here.

First, it’s possible that fever and
inflammation are correlated

purely by coincidence.

Or, there could be a causal relationship
that’s the opposite of what you think––

the fever causes the inflammation,

rather than the inflammation
causing the fever.

Or both could share a common
underlying cause you haven’t thought of.

If I may, just what do you think causes
inflammation? Nothing?

It just is? Really?

Humor me for a moment in discussing
one of your colleague’s ideas––

Dr. Oliver Wendell Holmes.

I know, I know, you don’t
like his theory––

you already wrote a scathing
letter about it.

But let’s fill your students in, shall we?

Holmes noticed a pattern: when a
patient dies of childbed fever,

a doctor performs an autopsy.

If the doctor then treats a new patient,

that patient often comes
down with the fever.

Based on this correlation between
autopsies of fever victims

and new fever patients,
he proposes a possible cause.

Since there’s no evidence that the autopsy
causes the fever beyond this correlation,

he doesn’t jump to the conclusion
that autopsy causes fever.

Instead, he suggests that doctors
are infecting their patients

via an invisible contaminant on their
hands and surgical instruments.

This idea outrages most doctors,
who see themselves as infallible.

Like Meigs here, who refuses to consider
the possibility

that he’s playing a role in
his patients’ plight.

His flawed argument doesn’t leave any
path forward for further investigation—

but Holmes’ does.

It’s 1847, and physician Ignaz Semmelweis

has reduced the number
of childbed fever deaths

in a clinic from 12% to 1% by requiring
all medical personnel

to disinfect their hands after autopsies
and between patient examinations.

With this initiative, he has proven
the contagious nature of childbed fever.

Ha!

It’s 1879, and Louis
Pasteur has identified

the contaminant responsible
for many cases of childbed fever,

Hemolytic streptococcus bacteria.

Hmm, my fries are cold.

Must be because my ice cream melted.