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Bradford Hill

correlation and causation

Correlation and causation between vaccines and adverse effects

Correlation and causation are topics that have become a part of the anti-vaxxer claims regarding the links between vaccines and adverse effects. I hear both terms thrown out so frequently, it’s hard to determine what is what.

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.

Correlation is a statistical technique that tells us how strongly the pair of variables are linearly related and change together. It does not tell us why and how behind the relationship but it just says a relationship may exist. 

Causation takes a step further, statistically and scientifically, beyond correlation. It is any change in the value of one variable that will cause a change in the value of another variable. It is often referred to as cause and effect.

But there are ways to establish causation from correlation. But it must happen with a logical process that does not resort to special pleading and pseudoscience

For example, biological plausibility is one of the requirements 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 the need for biological plausibility by using their own personal anecdote as “proof.”

That’s why science is much harder than pseudoscience. Establishing correlation and causation requires a strong knowledge of a scientific or medical specialty 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 correlation and causality.Read More »Correlation and causation between vaccines and adverse effects