Affecting public health has a few components. It includes providing a safe environment at home, at work, and in public spaces. It involves protecting the food and water supply from pathogens and toxins. Perhaps the most challenging component, however, is affecting people’s behaviors. Humans are complex psychological animals, and simply providing information to facilitate a rational decision may not always have the intended effect.

Those in power wishing to protect the public from themselves can simply pass laws that coerce people into safer behavior, such as seat belt laws and helmet laws. This approach amounts to outlawing certain unhealthy choices. There is also the “nudge” approach where the unhealthy choice is not outlawed, but the healthier choice is facilitated or made the default choice so that people have to work harder if they still wish to make the unhealthier choice for themselves.

Short of passing laws to force or nudge people in the right direction, the default approach to improving healthy behaviors is to provide information via either public service announcements or warning labels. How effective, however, are such measures?

A recent survey (all the usual caveats about the limitations of surveys apply) looked at various methods for increasing the intent of parents to vaccinate their children. This was a survey, not a measure of actual vaccine compliance, but the results are sobering nonetheless. 1,759 parents were surveyed:

Parents were randomly assigned to receive 1 of 4 interventions: (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 results were no what we would have hoped:

None of the interventions increased parental intent to vaccinate a future child. Refuting claims of an MMR/autism link successfully reduced misperceptions that vaccines cause autism but nonetheless decreased intent to vaccinate among parents who had the least favorable vaccine attitudes. In addition, images of sick children increased expressed belief in a vaccine/autism link and a dramatic narrative about an infant in danger increased self-reported belief in serious vaccine side effects.

None of the four messaging styles had a positive effect, they just had different kinds of negative effects. Most interesting, telling parents who tended to be anti-vaccine to begin with that the MMR vaccine is not linked to autism reduced their belief that MMR causes autism, but at the same time reduced their willingness to vaccinate a hypothetical future child from 70% to 45%.

Just like in the movie War Games, it seems the only way to win this game is to not play at all. The authors caution that, given vaccination rates overall are already quite high, any messaging about the safety of vaccines has a greater potential to inadvertently reduce vaccine compliance rather than increase it further.

The authors further speculate that the paradoxical result is due to the parents digging in their heels and being motivated to defend their initial vaccine negativity. This is consistent with other research (nicely summarized here by Chris Mooney) indicating that people will tend to react to new information that contradicts their existing beliefs by clinging to them even more tightly. The new information motivates them to think of other reasons to support their initial belief, in addition to reasons to dismiss the contradictory information. In the end they may be even more convinced of their original position.

The situation reminds me of the parable of the sun and the wind who decided to compete to see who could get a man to remove his coat. The wind tried to blow the coat off, but the harder it blew the harder the man held onto his coat. The sun then had its turn – it simply shined down on the man until he became warm and took off the coat.

In public messaging, we have to be more like the sun than the wind. A successful campaign would get people to want to engage in the healthier behavior, and perhaps even think it was their idea all along. Yes, this is psychological manipulation (just like all politics, by the way). Rational people have a knee-jerk negative reaction to the notion of such manipulation. We want to live in a world where giving people information is enough for them to make rational decisions, but that is not the world in which we live.

One approach, therefore, is benign psychological manipulation – making the healthy choice seem more desirable. One such approach is called social norming. This approach essentially leverages peer-pressure by telling people that most people do not engage in unhealthy behaviors, or do engage in healthy behaviors. It would therefore have been interesting if the above survey had a fifth group who were simply told – “most parents protect their children from infectious diseases by vaccinating them.” This is not deceptive, it is entirely true, but it is selected to coerce with positive peer pressure.

Such social norming campaigns are especially effective when people believe that an unhealthy behavior is more common than it actually is. Giving them correct information about actual prevalence of the behavior does seem to reduce the unhealthy behavior whereas warning people about the dangers of a behavior may just foster further belief that the behavior is more common than it is, which can actually increase the unhealthy behavior.


Public health campaigns have the potential to significantly increase the health of the public and reduce the cost of health care. We should not make naive assumptions about the efficacy of such campaigns, however. Like any other intervention, they will be most effective if they are evidence-based.

What the evidence is telling us so far is that public messaging can easily backfire if human psychology is not taken into account. Further, basic human psychology can be leveraged to have very successful public information campaigns.

There is, however, another approach. A public that had greater scientific literacy coupled with greater critical thinking skills would be more likely to respond rationally to simple information. This is not just an assumption – there are studies that show that skeptics are more likely to engage in analytic cognitive thinking and make fewer logical errors in their reasoning. Skeptics are also more likely to engage their inferior frontal gyrus, which is involved in cognitive inhibition.

In other words, when confronted with new information it is possible to inhibit the automatic response to defend one’s existing beliefs, and to engage in the hard work of analytic thinking and metacognition. A greater emphasis on teaching such critical thinking skills would therefore create a populace that is better prepared to receive future messaging about healthy and unhealthy behaviors.



Posted by Steven Novella