It’s fitting that as Donald Trump continues to flirt with anti-vaccine conspiracy theories, inoculation may provide the key to effectively debunking this sort of misinformation.

That’s the finding of a new study published in Global Challenges by Sander van der Linden, Anthony Leiserowitz, Seth Rosenthal, and Edward Maibach. The paper tested what’s known as “inoculation theory,” explained in the video below by John Cook, who’s also published research on the subject. The video is a lecture from the Denial101x free online course, which itself is structured based on inoculation theory:



John Cook Denial101x lecture on inoculation theory.

According to inoculation theory, facts are important but by themselves aren’t sufficient to convince people as long as misinformation is also present. People also have to be inoculated against the misinformation, for example through an explanation of the logical fallacy underpinning the myth.



To test the theory, the study authors ran an experiment using a fact that’s been subjected to a tremendous misinformation campaign: the 97% expert consensus on human-caused global warming. There’s been some debate among social scientists about consensus messaging, with most research suggesting it’s effective and important at convincing people about the importance of climate change.



However, Dan Kahan has argued that given science communicators’ efforts over the past decade to inform the public about the expert consensus, the fact that so few people are aware of it suggests that consensus messaging is a dud. If it were going to work, it should have worked by now, the argument goes.

This new study guts that argument. In their experiment, the scientists first asked their representative American subjects “To the best of your knowledge, what percentage of climate scientists have concluded that human-caused climate change is happening?”. The average answer was between 70% and 73%. Each group was then presented with evidence of the 97% expert consensus. That raised the average answer to about 90%. As you would expect, facts were effective when presented by themselves.



The authors ran three more tests. First, after showing the 97% consensus evidence in pie chart form, they then presented a group with a piece of misinformation – the infamous Oregon Petition, which is often used to argue there is no climate consensus. This misinformation completely offset the influence of the facts – the subjects’ answers in this group fell all the way back down to a 73% perceived consensus.

In the next tests, after showing the evidence of 97% consensus, the scientists “inoculated” the groups against the misinformation. In one test, they informed the group “Some politically-motivated groups use misleading tactics to try to convince the public that there is a lot of disagreement among scientists.” In the final test, they provided much more detail about the specific flaws in the Oregon Petition, and how it misinforms people.



After then showing these groups the Oregon Petition misinformation, the average perceived consensus rose to 80% in the first test, and 84% in the second test. The inoculation offset about half to two-thirds of the effect of the misinformation, and participants’ perception moved closer to the truth.

As lead author Sander van der Linden explained, the effectiveness of the inoculation across the political spectrum was particularly encouraging:

We found that inoculation messages were equally effective in shifting the opinions of Republicans, Independents and Democrats in a direction consistent with the conclusions of climate science. What’s striking is that, on average, we found no backfire effect to inoculation messages among groups predisposed to reject climate science, they didn’t seem to retreat into conspiracy theories. There will always be people completely resistant to change, but we tend to find there is room for most people to change their minds, even just a little.

As John Cook put it:

The intriguing result was the inoculation worked across the political spectrum - even among conservatives - which tells me that nobody likes to be deceived.

These results suggest that consensus messaging hasn’t been terribly effective at changing peoples’ minds about climate change because there’s been a simultaneous misinformation counter-campaign, articulated by Republican strategist Frank Luntz in his infamous leaked memo:

Voters believe that there is no consensus about global warming within the scientific community. Should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly. Therefore, you need to continue to make the lack of scientific certainty a primary issue in the debate.

Those who oppose taking action to curb climate change have heeded Luntz’s call. “There is no consensus” is the fourth most popular myth in the Skeptical Science database. An analysis of climate editorials published by conservative columnists between 2007 and 2010 found that “no consensus” was far and away the most popular myth, made in a whopping 64% of their climate editorials. The climate consensus misinformation campaign has been robust, and as in van der Linden’s study, canceled out much the effect of the 97% consensus fact.

The challenge then is in delivering the facts and inoculation to the individuals who are being exposed to the misinformation. Conservative media outlets are the primary climate misinformation delivery system, but are unlikely to also publish facts and explanations about why their misinformation is wrong. However, while individuals who rely solely upon biased media outlets may be incurable, the majority of the public could potentially be inoculated against misinformation.

The study thus provides a key message for those fighting against the growing post-truth, “alternative facts” culture: facts by themselves are insufficient, but explaining the flaws underpinning associated misinformation can help weaken its effect and increase public acceptance of the facts. The fact-myth-fallacy debunking structure explained and implemented in the Denial101x free online course is thus a valuable tool for scientists, science communicators, and anyone struggling to break through ideological barriers to facts.