I originally wrote this article in 2014 to discuss whether correlation implies causation. Not that I expect everyone to read and remember this one article, but it’s frustrating when I see a conversation where people who deny science and accept science both misuse correlation and how it relates to causation. So, I decided to update this article and republish it as a reminder that the relationship of correlation to causation isn’t as easy as a simple trope or meme.
One of the foundations of biomedical science is whether correlation implies causation. Anti-vaccine activists often conflate or misunderstand the two, rejecting or accepting correlation as it fits its narrative. The “correlation implies causation” story is often abused, misused and confused by many writers.
One thing we do know about correlation is that if you can’t establish correlation, despite numerous attempts, it is nearly impossible to claim causation. Also, if you do observe correlation, it also doesn’t imply causation.
But there are methods, grounded in powerful science, to establish causation from observations of correlation. So sometimes correlation does not imply causation. But sometimes correlation implies causation.
This article will help show how we may be able to establish causation from observations of correlation. And, like all science, this is hard stuff. Continue reading “Correlation implies causation – when it does or does not with vaccines”
In 2014, I reported on an outbreak of a mysterious viral disease that exhibited polio-like symptoms. At the time, around 23 children and young adults were afflicted with this polio-like syndrome, known as acute flaccid myelitis. Since then, a total of around 350 individuals have been stricken by the acute flaccid myelitis from 2014 through 2018.
Recent reports of another outbreak of acute flaccid myelitis in Minnesota has brought out zombie memes pushed by the anti-vaccine religion, they blame acute flaccid myelitis on the polio vaccine. Of course, these bogus claims aren’t based on any scientific evidence, but that’s never stopped the anti-vaccine zealots.
These outbreaks have caused the public health sleuths to search for the actual causes of this polio-like syndrome. And there just isn’t any robust or valid evidence that the polio vaccine is any way related to acute flaccid myelitis.
As we know, polio can be a crippling and potentially deadly infectious disease caused by the poliovirus, a human enterovirus, that spreads from person to person invading the brain and spinal cord and causing paralysis. Because polio has no cure, the polio vaccine is the best way to protect ourselves from the crippling disease.
The United States last experienced a polio epidemic in the 1950s, prior to the introduction of the polio vaccine 60 years ago. Today, polio has been eradicated from most of the planet, as the number of worldwide polio cases has fallen from an estimated 350,000 in 1988 to 113 in 2017 – a decline of more than 99% in reported cases.
Because real scientists wanted to know what caused this acute flaccid myelitis outbreak, they tried to hunt down the actual cause. And that’s when they landed on enterovirus 68, a once-rare virus. As we always do, we’ll look at the facts behind this virus and it’s relationship to polio (or polio vaccines).
Continue reading “Acute flaccid myelitis – enterovirus to blame according to new CDC report”
How many times have you heard tiresome tropes about the HPV vaccine causing this or that? No matter how many times we debunk the nonsense, it persists. One of the critical points I try to make is that before an anti-vaccine claim can be made, there has to be a biological plausibility. That is, can we establish a reasonable and plausible biological mechanism, without resorting to special pleading and pseudoscience, that can lead one from one action, say receiving a vaccine, to some result, real or imagined.
Biological plausibility is a requirement to establish that correlation means causation. It is almost an essential requirement for one to claim a causal association. But biological plausibility must be consistent with our existing knowledge of biology, chemistry, physics, and medicine. How many times has an anti-vaccine zealot tried to convince us that “mercury in vaccines causes autism” but ignores the basic scientific tenets of numerous fields of biomedicine like biochemistry, cell biology, toxicology, immunology, neurology – well, just about every field?
Or someone who claims that acupuncture treats a bunch of diseases, yet we cannot find any reasonable biological plausibility between sticking a needle in the arm to treating some medical condition like pain. They tend to ignore that by using their own personal anecdote as “proof.”
That’s why science is much harder than what is said by the pseudoscience pushers. Establishing plausibility requires a strong knowledge of science to make the case. It’s much more than simply stating that plausibility does exist, you have to use actual real science, published in real scientific journals, to make the case.
So let’s talk a little bit about causality. And a large dose of biological plausibility. Continue reading “Biological plausibility – a keystone of medical and vaccine research”