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

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It's 1843, and a debate is raging about one of the most common killers of women: childbed fever— no one knows what causes it. One physician has observed patients with inflammation go on to develop childbed fever, and therefore believes the inflammation causes the fever. What's the problem with this argument? Elizabeth Cox explores the false cause fallacy and how to dissect claims with skepticism.

Lesson by Elizabeth Cox, directed by TOGETHER.

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.