healthHealth and Medicine

This Psychological Effect Explains Why Anti-Vaxxers Believe What They Believe


Robin Andrews

Science & Policy Writer


Vaccines save lives on a daily basis, and science doesn't care if you think otherwise. panpilai paipa/Shutterstock

Of all the cognitive biases that we encounter on a daily basis, few could be as culturally relevant as the Dunning-Kruger Effect (DKE). This describes those that have a poor understanding or low level of ability with regards to a certain subject thinking that the very opposite is in fact true. A new Social Science & Medicine study has concluded that anti-vaxxers suffer from the DKE in spades, which makes dealing with them more complex than many have previously thought.

Originally described by social psychologists Justin Kruger and David Dunning back in 1999, it’s elucidated most eloquently in a 2011 chapter of a treatise composed by the latter. It’s all about meta-ignorance: the person’s ignorance of ignorance. “The scope of people's ignorance is often invisible to them,” Dunning explains, citing experimental data that first brought the effect to light.


Those suffering from DKE are left with a double burden: “not only does their incomplete and misguided knowledge lead them to make mistakes, but those exact same deficits also prevent them from recognizing when they are making mistakes and other people choosing more wisely.”

This new study, spearheaded by postdoctoral researcher Dr Matt Motta at the University of Pennsylvania's Annenberg Public Policy Center, points to anti-vaxxers as a prime example of this phenomenon, after having investigated it for the very first time.

Anti-vaxxer sentiment has been around for some time, but this problem – one that’s a genuine threat to the lives of millions, particularly the young – appears to have been on the rise in the last few years. Hinting at why this may be, Motta et al. start their paper with a mention of the President’s push to get a prominent anti-vaxxer, Robert Kennedy Jr., to start a committee to look at the safety of vaccines.

Clearly, the spread of misinformation by prominent figures is exacerbating the problem, but what about the anti-vaxxers themselves? What do they believe? Prior studies suggest that members of the public that are anti-vaxxer inclined have disgust-based moral purity “concerns”, but does the DKE rear its ugly head too?


The team hypothesized that those with low awareness and understanding of autism will be the most likely to think they are best informed – better than actual experts in the field, in fact – on the subject. In order to test out the extent of this overconfidence, the team surveyed 1,310 US adults, a nationally representative sample.

They tested their autism awareness by asking them questions – developed by the National Alliance for Autism Research – about the condition, while also asking: “Can vaccines administered to children at young ages cause them to become autistic?” The subjects were also queried as to whether they knew more of less than medical doctors, and scientists, about autism.

Anti-vaxxer policy attitudes were also assessed based on the response to the following statement: “Parents should be able to decide NOT to vaccinate their children against measles, mumps, and rubella.”

Remarkably, a large proportion of respondents thought they knew more than doctors (36 percent) and scientists (34 percent) about autism causes. Unsurprisingly, those with the highest level of overconfidence both endorsed vaccine misinformation the most and knew the least about autism.


Interestingly, overconfidence was associated with increased support for the role that non-experts, such as celebrities (including the President) play when it comes to making policy on vaccines. It's also linked to opposition to mandatory vaccination policies.

So it's safe to assume then that your estranged family member spouting such nonsense on Facebook is probably suffering from an acute case of DKE. How, then, can we vaccinate society against this insidious representation of it?

“We recognize that more knowledge about autism and less misinformation about vaccines may not completely ‘eradicate’ the existence of anti-vaccine sentiment,” lead author Motta told IFLScience. Although important, this study clearly found that we need to tackle the overconfidence of anti-vaxxers too.

“What those efforts might look like, however, is an open empirical question – and one my research team and I are actively investigating.”


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