Have you ever wondered how related the number of people
that drown in pools each year is
to how many Nicolas Cage films are released at the same year?
Turns out the 66.6% correlation between the two
or how about the fact that there is 99.26% correlation between the divorce rate in Maine
and the per capita consumption margarine
or %99.79 correlation between spending on science, space and technology
and the number of suicides by hanging, strangulation and suffocation.
Just because there is a correlation between too variables doesn't mean
that one causes the other.
This assumption is a logical fallacy
and yet we are drawn to headlines like
"People who have more sex make the most money."
Unfortunately "this" does not always equal "that".
Even though it may look like it cheese consumption probably isn't related to
how many people died tangled in their bedsheets.
But sometimes isn't so obvious.
Numerous studies found that menopausal women taking hormone replacement therapy
had a lower than average incidence of heart disease.
Leading doctors to believe that hormone replacement could protect against heart disease.
However when women underwent randomized controlled trials
they found that hormone replacement therapy actually increased the risk of heart disease.
When the original data was finally reanalysed, it was found that
women who took the therapy were of a higher socio-economic group
with a better diet and exercise regime.
This was the real cause behind decreased risk of heart disease.
Another case found that those who used nightlights as a kid were more likely to develop myopia.
But there is actually strong link between parenatal myopia
and the development of child myopia so in reality myopic parents simply more likely
to leave light on in their child's bedroom.
These are examples of lurking variable where A does not cause B
but rather C causes them both.
It's a little like taking people who have lung cancer
and thinking "Hey, they all carrying lighters in their pockets
so lighters must cause cancer."
While not realizing that smoking is the confounding variable.
And scientists worked hard in their studies to try avoid this.
But it gets worse when popular media takes advantage of these potentially coincidental correlations.
And one study about chocolate weight-loss connection was actually designed as
a way to expose how science reporting can be sensationalized.
A science writer with a PhD in Microbiology ran a real clinical trial
where participants were assigned to three groups.
A low carb diet, a low carb diet plus a 1.5 ounce chocolate bar
and the group that maintains their regular diet.
At the and of three weeks, the chocolate group did lose the most weight
but the journalists consciously used terrible science.
He used 15 participants and measured 18 different measurements including weight loss
cholesteral, sleep quality, blood pressure, well-being etc
and when you use small group of people and measure a large number of things
you're pretty much guaranteed to get a statistically significant results
which Veritasium has an amazing video on here if you wanna check out.
The result could have easily been something different
such as chocolate correlates to lower blood pressure.
If the study had been peer-reviewed by other researchers
it would've been called out
so instead he submitted it to a journal for a fee 600 Euros
making up a fake instutition name.
The Institute of diet and health.
He then sent out a press release to dozens of the media publications
and very quickly getting slim by chocolate was front page news.
With that in mind however we can't dismiss correlation entirely.
Correlative evidence is an essential part of science.
Double-blind studies are not always possible or ethical to run
often leaving correlation is the best evidence available.
When every possible causative relationship is systematically explored
correlation can be use as a powerful tool for assessing cause and effect relationships
and progressing science even further.
Big thanks to Tyler Vigen for providing his charts on this interesting correlations.
You can check out his website or his book "Spurious Correlations" for more peculiar examples
and subscribe for more weekly science videos every Thursday.