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Correlation versus causation

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Correlation versus causation

Getting the two terms confused is forgivable for a lay person but pharmacists should know the difference, says Peter Kelly

A number of years ago, I was making my way to Glastonbury with a friend when he said he wanted to stop off at a pharmacy on the way. I asked what for. He said he wanted a get a razor before we got to the music festival.
I told him not to be ridiculous. There was no way he was going to shave while at Glastonbury. We were going to be living in mud on a diet of cider and cheese chips.
I had no intention of even showering for the weekend, never mind shaving. He then said he wanted to shave because whenever he did not shave, he got cold sores. Initially I thought he was joking.
I then explained that he was not getting cold sores due to not shaving. It was a case of correlation not causation. It was likely that the only times he was not shaving were when he was away for the weekend or at a music festival and other similar event where he was over-drinking and under-sleeping, and the cold sores were due to his immune system being overwhelmed.
He thought about it for a minute, then replied: ‘Yeah, you are right. I don't know what I was thinking.’ He was not the first and will not be the last to mistake correlation with causation.
Now to the present day: a pharmacist in Ireland is facing two allegations of professional misconduct over a social media post which appeared to support an anti-vaccination group. The PSI fitness-to-practice committee heard claims that the pharmacist shared a video from an anti-HPV vaccine group.
The video claimed that several young girls suffered severe conditions after they were given the vaccine, Gardasil, to protect against the HPV virus, which is a known cause of cancer, particularly cervical cancer.
The pharmacist is also accused of liking a comment that stated: ‘Wouldn't be giving that vaccine to my daughter. It is not safe.’
It is an interesting case. Getting confused about correlation and causation is forgivable for a lay person, particularly if there is personal trauma or loss involved. However, pharmacists should know the difference and they should be very clear that about the world of difference between a professionally conducted clinical trial and a couple of cases of anecdotal evidence.
The dispensing of misinformation can be just as dangerous as the dispensing of an incorrect medication. As a professionally trained pharmacist you cannot argue against peer reviewed clinical studies based on your own personal opinion and a couple of personal anecdotes.
If someone reports what they believe is a side effect or negative outcome to a vaccine or other medication you can, of course, report it through the yellow card scheme. But you have to be very careful about drawing conclusions about medication that are based on your opinions and contradictory to the findings of clinical trials.
Pharmacists must be particularly careful when speaking about vaccines because vaccine safety, for whatever reason, has become a highly politicised issue. It is not a political issue: the safety and efficacy of vaccines is a clinical issue guided by clinical trials and studies conducted by highly trained professionals in a standardised way. It is not a political debate as some people believe.
Again, it is forgiveable for lay people to somehow fall for the delusion that it is a political debate. It should go without saying that pharmacists, as trained scientists, do not see it as anything of the sort.
We live in politically volatile times. We live in exciting times. We are living through a period of incredible technological change. Times of great change always create political instability as they have the potential to upset and change the status quo in frightening and unpredictable ways.
Every society will always have an element that is anti-science. We live in an extremely competitive world, and the winners and losers in a scientifically literate country are very different from those in a superstitious and dogmatic country. We always have to be vigilant against attacks on evidence-based thinking. A pharmacist who does not believe in evidence-based medicine is like a priest who does not believe in God.
The evidence in favour of the use of licensed vaccines is overwhelmingly positive. As pharmacists our views and opinions on matters of medicines, vaccines and health issues carry more weight than non-professionals. As pharmacists we know that the success of all modern medicine is built on the foundation of evidence-based decision making.
If you are going to publicly say something that contradicts that evidence, you are going to need a very good reason for doing so.

Peter Kelly is a community pharmacist based in London and occasional stand-up comedian.

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