Anecdotes as Evidence

Evidence is evidence, right?

Not really.

There is a hierarchy of evidence, from weakest to strongest, that help folks make decisions about science and medicine.

In an age when everything is evidence of something, remember that anecdotes are not scientific evidence.

That’s why you can’t just search PubMed, read abstracts, and say that you have done your research. For any study, you have to review and judge the quality of the evidence it provides.

Is it a case report (a glorified anecdote), case series, or animal study (lowest quality evidence) or a systemic review or meta analyses (highest quality evidence)?

What about case control studies, cohort studies, and randomized controlled trials? They lie somewhere in between on the hierarchy of evidence scale.

Anecdotes as Evidence

And where do anecdotes fit in?

“Anecdotes are uncontrolled subjective observations. I have often criticized reliance on anecdotes, which is especially problematic in medicine. The problem with anecdotes is that they are subject to a host of biases, such as confirmation bias. They are easily cherry picked, even unintentionally, and therefore can be used to support just about any position. For every anecdote, there is an equal and opposite anecdote.”

Steven Novella on The Context of Anecdotes and Anomalies

Anecdotes are not scientific evidence.

Unfortunately, some people use anecdotal evidence to make some very serious decisions, including skipping or delaying their children’s vaccines, leaving them unvaccinated and unprotected.

“An anecdote is a story – in the context of medicine it often relates to an individual’s experience with their disease or symptoms and their efforts to treat it. People generally find anecdotes highly compelling, while scientists are deeply suspicious of anecdotes. We are fond of saying that the plural of anecdote is anecdotes, not data.”

Steven Novella on The Role of Anecdotes in Science-Based Medicine

Believing that anecdotes are important scientific evidence is also what often drives some pediatricians to pander to fears that parents may have about vaccines, helping them create non-standard, parent-selected, delayed protection vaccine schedules.

What else do you need to know about anecdotal evidence?

Anecdotes are basically the fuel of the anti-vaccine movement.

“With little or no evidence-based information to back up claims of vaccine danger, anti-vaccine activists have relied on the power of storytelling to infect an entire generation of parents with fear of and doubt about vaccines. These parent accounts of perceived vaccine injury, coupled with Andrew Wakefield’s fraudulent research study linking the MMR vaccine to autism, created a substantial amount of vaccine hesitancy in new parents, which manifests in both vaccine refusal and the adoption of delayed vaccine schedules.”

Shelby et al on Story and science

Well, anecdotes and fear – often combined in vaccine scare videos.

If you have been making your vaccine decisions based on anecdotes, it is time to do a little more research and get better educated about vaccines.

What to Know About Anecdotes as Evidence

Anecdotes, although they are easy to believe, are not scientific evidence, and certainly shouldn’t persuade you that vaccines aren’t safe, that vaccines aren’t necessary, or that vaccines are associated with autism.

More on Anecdotes as Evidence


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