Aug 04 2015

Convincing Antivaxxers

A new study has been published in PNAS exploring methods for changing the attitudes of those who are anti-vaccine. The results differ from a previous study published last year in Pediatrics. Let’s explore their methods and results.

Both studies questioned subjects about their attitudes toward vaccines and their willingness to vaccinate their children. The Pediatrics study was web-based and recruited 1759 parents. They divided them into four groups:

(1) information explaining the lack of evidence that MMR causes autism from the Centers for Disease Control and Prevention; (2) textual information about the dangers of the diseases prevented by MMR from the Vaccine Information Statement; (3) images of children who have diseases prevented by the MMR vaccine; (4) a dramatic narrative about an infant who almost died of measles from a Centers for Disease Control and Prevention fact sheet; or to a control group.

The PNAS study was in person, but only recruited 315 subjects. They divided people into three groups: 1) given information debunking vaccine myths, 2) told about the risks of measles and shown graphic images, 3) control group given information unrelated to vaccines.

The Pediatrics study found that, for the strongest anti-vaccine views at baseline, none of the four groups were significantly affected in terms of their willingness to vaccinate. The groups warned about vaccine-preventable diseases and shown images of sick children changed their beliefs about vaccines somewhat, but this did not translate into a significant change in intent to vaccinate (again, for the strongest anti-vaccine subjects at baseline).

The PNAS study showed the same result for the group in which vaccine myths were countered with scientific information, but they found that the group given information about measles, for example, did increase their willingness to vaccinate. This last result may contradict the Pediatrics study (it depends on how comparable the groups were).

What does this mean?

Taken together the studies indicate that simply giving people scientific information that contradicts myths they already strongly hold is ineffective in changing their beliefs. Or, even if they do change their belief, they won’t change their behavior but just find another justification. This is consistent with results from other studies which found that giving people factual information that contradicts their strongly held beliefs actually causes some to dig in their heels and strengthen their now debunked belief.

This has been termed the “backfire effect.”  Most of the research has involved political views, and suggests that when someone holds a belief strongly with emotional conviction, facts alone are unlikely to change their mind. In fact, by challenging them you engage their defense mechanisms which strengthen their convictions.

People engage in a number of strategies in order to maintain their strongly held beliefs against the evidence. Collectively these strategies are called “motivated reasoning.” They include strategies such as calling into question the power of science itself, or the power of science to address the specific topic of their beliefs (the scientific impotence argument).

Engaging in conspiracy theories, of course, is the bread and butter of motivated reasoning. Conspiracies solve all problems – they can be used to dismiss all inconvenient evidence, and explain the absence of evidence, the apparent scientific consensus, the lack of mainstream media attention, and the absence of evidence for the conspiracy itself. It is also extremely easy to twist facts and behavior to make them seem sinister.

These are all powerful psychological phenomena, that overwhelm dry scientific facts. Keep in mind, however, that this only applies to emotionally held beliefs. If we don’t particularly care about a certain conclusion, or if the science fits our world view, then we are happy to listen to the science. (You only get credit for being scientific, however, when you accept the science that goes against your strongly held or ideological beliefs.)

The two studies disagree on the effects of fear in motivating parents to vaccinate their children. The Pediatrics study found that scientific information, images, and narratives were equally ineffective. The information seemed to give the parents in the study pause, but they still held onto their fears of vaccines and did not change their willingness to vaccinate. The PNAS study found that combining scientific information with images did have an effect.

Clearly more research is needed. It seems that context and venue are likely to have a significant effect. Perhaps subjects felt more pressure to conform to information when they were present in person, rather than online. We also don’t know how long the effect will last – does it fade after a couple of days? Finally we don’t know if any intervention will actually change vaccination rates out in the world. Right now we only have data from contrived study situations.

There is good reason to suspect, however, that countering fear with fear is likely to be more effective than countering fear with dry science. Of course this all depends on how strongly held the anti-vaccine beliefs are. For the most ardent vaccine deniers, I doubt anything with have a significant effect.

Where do we go from here?

The one thing that is clear from all of this scientific evidence is that humans as a species are rather pathetic on average. We are emotional creatures that, by default, can easily render ourselves immune to logic and facts whenever our emotions are at stake. It is hard not to feel that this is the source of endless mischief and sorrow for humanity. How do we fix it?

The ultimate solution, in my opinion, is to promote scientific skepticism. The skeptical outlook is to consciously remove oneself from any emotional investment in any particular belief. Instead we align our identity with the process of science, listening to facts, and following valid logic and sound arguments.

Part of this is being transparent and engaging intellectually with others. The critical analysis of others will keep us honest. We must be our own harshest skeptic, for if not others will expose any flaws in our process. We will then be under pressure to examine our methods and change our conclusions if necessary. Essentially being a skeptic and being part of a community of skeptics harnesses inherent human psychology toward being logical and scientific, rather than irrational and emotional.

As a skeptic my primary motivation is getting it right (not defending any particular position), and if I don’t I know that other skeptics will point out my error, and if I don’t properly engage with their criticism, or if I dig in my heels, I will lose credibility.

Further, it’s important to simply give people an internal desire to value the truth, honesty, transparency, and following a valid process. The desire, however, is just the beginning. We also need to spread the tools of critical thinking. It’s a lifelong journey, and it’s not easy. It takes constant vigilance and self-examination.

The more skeptical the world is, however, the better off we are. The less motivated reasoning and nonsense there will be in the world.

Making the public more skeptical and scientifically literate is changing the game, but it’s a generational struggle. Meanwhile, we still have to deal with important issues like public health. These studies suggest that we may need to use a variety of strategies, which include warning people about the dangers of vaccine preventable diseases.

There is an entirely different set of psychological studies, however, that suggest that the “scared straight” approach does not work at all. Any effects are short lived. Therefore the entire approach of both of these studies is flawed. They are considering scientific information vs using fear, but there is a third way.

Within health care and public health researchers are exploring that third way, which can be called social norming. This approach tries to motivate people to engage in more healthy behaviors by emphasizing that most people engage in these behavior – essentially using social pressure to change behavior. These techniques are proving more effective than the scared straight method.

With individuals, researches are exploring what is called motivated interviewing – asking questions so that individuals state their goals, then exploring how to achieve those goals. This engages people in a way that makes them feel self-empowered and self-motivated, and also provided some social pressure to appear consistent. You just said you wanted your children to be safe and healthy, so will you take a simple step to protect them from disease?

Social norming and motivated interviewing are still exploiting human psychology and you might think of this as manipulation. There is validity to this view, but you can also look at it this way: human psychology will be involved one way or the other, you might as well give information in a manner that engages human psychology constructively rather than counter-productively. With both methods you are never lying or giving false or misleading information. You are simply presenting it in a manner that is compatible, rather than in conflict with, the likely emotions of the target.


Changing attitudes and behavior is remarkably difficult. The naive assumption that most people will respond to scientific information has proven over and over to be false. People are different in this regard, but for most people they will respond to science when it does not conflict with their emotions, and they will deny science with motivated reasoning when it does conflict.

Don’t think of this as true-believers vs rationalists. We are all true-believers some of the time, and rationalists at other times.

The goal is to give people the tools and the motivation to be rational more of the time. Meanwhile, while trying to engage with the public over important issues like public health, we need to frame our information so that it will actually have a positive effect. To ignore human psychology while trying to change behavior is folly.

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