Correlation implies causation – when it does or does not with vaccines

correlation implies causation

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”

Biological plausibility – a keystone of medical and vaccine research

biological plausibility

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”

Pseudoscience is bullshit and science is definitely not

pseudoscience is bullshit

Pseudoscience and science – the former is a belief system that uses the trappings of science without the rigorous methodologies that values evidence. The latter is an actual rational methodology to discover facts about the natural universe. Pseudoscience is bullshit. Science is rational knowledge.

Pseudoscience is seductive to many people partially because it’s not only easy to comprehend, but also because it creates black and white false dichotomies about the natural universe. This fake science is the basis of alternative medicine, astrology, and many other “fields” that true believers try to say is science.

Pseudoscience tries to make an argument with the statement of “it’s been proven to work”, “the link is proven”, or, alternatively, they state some negative about scientifically supported therapies. It really  has an appeal to it because it digests complex analysis to a simple “yes, this works.”

Alternative medicine relies on this pseudoscience by creating the illusion that medicine can be really easy if you drink this kale shake, and you will have 100% chance of avoiding all cancer. Real science based medicine provides real clinical information about every cancer, how it can be treated, and what the real prognosis is.

Acupuncture, chiropractic, homeopathy, naturopathy, and many other “alternative medicine” beliefs are pseudoscience. They simply lack robust evidence to support their efficacy.

For example, real science has debunked the “there is a proven link between vaccines and autism,” a common and rather dangerous belief.  Real science has failed to establish the clinical usefulness of most alternative medicine (CAM) therapies.

We will also explore what exactly makes an idea scientific (and spoiler alert, it isn’t magic), and contrary the logic of science, what makes an idea “pseudoscientific.” So sit down, grab your favorite reading beverage, because this isn’t going to be a quick internet meme. Pseudoscience is bullshit, and let me show it to you. Continue reading “Pseudoscience is bullshit and science is definitely not”

European court vaccine ruling – the vaccine deniers think they won

European court vaccine ruling

On 21 June 2017, the European Court of Justice ruled in favor of the plaintiffs in a case that examined whether Sanofi-Pasteur’s hepatitis B vaccine caused multiple sclerosis (MS) in a patient. Although the ruling might, on the surface, be considered bad for vaccines, we need to look more carefully at that European court vaccine ruling.

There are several questions that we need to answer. First, what did the court actually rule? What can courts say about science? And, is there any evidence that the hepatitis B vaccine causes multiple sclerosis? Continue reading “European court vaccine ruling – the vaccine deniers think they won”

MMR vaccine and autism – more high quality evidence that they are unrelated

MMR vaccine and autism

I have been unwavering on this one point – there is no link between the MMR vaccine and autism spectrum disorder (ASD). They are simply unrelated, based on high quality evidence published in respected peer-reviewed journals across the world. To dispute this conclusion, using only low quality evidence published in predatory and low impact factor journals, is the epitome of science denialism.

There are some interesting early results from a study, published in Nature, that is examining brain development in infants who are at risk for autism spectrum disorder. The study hasn’t uncovered any new information about what may cause autism, but it did confirm that the MMR vaccine is unrelated to autism. Throw this study onto the mountain of evidence that completely debunks that myth.

The ongoing study’s results indicates that changes in the brain in early infancy may be predictive of an autism diagnosis at age 2 in children who have higher odds of autism because an older sibling has been diagnosed with ASD. The researchers took MRI images of the brains of children at higher risk at ages 6, 12, and 24 months, along with administering a test at age 24 months that assists in the diagnosis of autism along with another test that evaluates social skills.

The early results (the final paper will come out within a year or two) suggests that rapid growth of the surface of the cerebrum from ages 6-12 months preceded an increase in brain volume at age 12-24 months in children at risk for ASD and who were diagnosed with ASD at 24 months. Based on this cortical surface growth, the researchers were able to predict an ASD diagnosis in 81% of high risk children who eventually were diagnosed with ASD.

Again, this study didn’t provide us with any information about possible causality for ASD – it provides us some evidence of predictive diagnostic methods. Moreover, the study had a relatively low study population, and we really need repeated studies to confirm the value of this study.

Emily Willingham, writing in Forbes, does a rather thorough review of the study for those interested in the predictive ability of the study. She says this about what this study says about any relationship between the MMR vaccine and an ASD diagnosis:

Finally, these changes before age 12 months that are associated with a later autism diagnosis precede the timing of administration of the MMR vaccine. This vaccine, readers may recall, is the one that true-believer anti-vaccine activists consistently promote as causative in autism. According to the vaccination schedule, it is administered at age 12 months. These latest detected changes arise before that age, but the rapid growth associated with them kicks in right at about age 12 months, once again illustrating that coincidence of events doesn’t always mean their association.

Dr. Willingham states that the changes that precede a diagnosis of autism appear well before the first administration of the vaccine. The first MMR vaccination just happens to be coincidental to the rapid growth that is associated with ASD. Remember correlation doesn’t imply causation, especially now that we have evidence that the brain changes indicated in ASD occur prior to administration of the MMR vaccine.

I know that the “true-believer anti-vaccine activists” will be unconvinced by this evidence, and that is sad. There is simply no evidence that MMR vaccine and autism are related. In fact, evidence suggest that they are not related.

The MMR vaccine saves lives, so let’s just protect our children with it.

 

Key citations

  • Hazlett HC, Gu H, Munsell BC, Kim SH, Styner M, Wolff JJ, Elison JT, Swanson MR, Zhu H, Botteron KN, Collins DL, Constantino JN, Dager SR, Estes AM, Evans AC, Fonov VS, Gerig G, Kostopoulos P, McKinstry RC, Pandey J, Paterson S, Pruett JR, Schultz RT, Shaw DW, Zwaigenbaum L, Piven J; IBIS Network.; Clinical Sites.; Data Coordinating Center.; Image Processing Core.; Statistical Analysis.. Early brain development in infants at high risk for autism spectrum disorder. Nature. 2017 Feb 15;542(7641):348-351. doi: 10.1038/nature21369. PubMed PMID: 28202961.


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Correlation does not imply causation – except when it does.

correlation

Editor’s note – this article has been substantially updated, and the new version has been republished here.

One of the central tenets of the pro-vaccine world is that correlation does not imply causation – but it is misused and frequently abused by many writers. We, the pro-science/pro-vaccine world, dismiss correlation, if real correlation can be shown, as robust evidence indicative of any causal relationship.

Conflating causation and correlation is somewhat different than the logical fallacy of post hoc ergo propter hoc, where one thinks one event follows the first event because of the existence of the first event. I’m sure all good luck charms and superstitions, like walking under a ladder, are related to the post hoc ergo propter hoc fallacy. So if I walk under a ladder, then trip on a black cat, then crash into a mirror, I don’t immediately blame the initial act of walking under the ladder. I just assume I’m clumsy.

Correlation and causation are a very critical part of scientific research. Basically, correlation is the statistical relationship between two random sets of data. The closer the relationship, the higher the correlation. However, without further data, correlation may not imply causation, that the one set of data has some influence over the other. Continue reading “Correlation does not imply causation – except when it does.”