Thursday, 3 May 2012

Strong reassurances about vaccines can backfire

Unwarranted public anxiety about vaccinations can have deadly consequences. Unfortunately, the challenge of communicating health risks is full of psychological complexity. A new German study brings this home, showing how messages that deny vaccination health risks in unequivocal terms can backfire, actually increasing concern among parents.

Cornelia Betsch and Katharina Sachse recruited 115 participants online (mean age 34; 34 per cent were male; 43 per cent had one or more children). The participants were asked to imagine they were a parent of an 8-month-old and to read an account of a fictitious illness Phyxolitis pulmonis. They were further told that their paediatrician had advised vaccinating their child against this condition. Next, the participants were presented with anti-vaccine statements that they'd ostensibly found on the internet (e.g. "Multiple vaccines overwhelm the infant's immune system"). Finally, they read statements of reassurance about the vaccine, which claimed any risks were low - half the participants read weak versions (e.g. "There is only sporadic evidence that repeated vaccinations overwhelm the immune system") and half read strong versions of these statements (e.g. "there is no evidence that repeated vaccinations overwhelm the immune system").

The key finding here was that participants who read the strong statements of reassurance actually reported greater perceptions of risk afterwards, and lower intentions to vaccinate their child. This effect was heightened among participants who had a preference for complementary medicine. Results didn't vary according to whether participants were a parent in real life or not.

A second study with a further 119 participants was similar but this time the source of the reassuring statements was varied, either being from a pharmaceutical company (untrusted) or from a government health department (a trusted source). Again, strong statements of reassurance backfired, increasing risk perception and reducing vaccination intentions, but only if those statements came from an untrusted source. Again, this paradoxical effect was stronger among participants who favoured complementary medicine.

This study can't reveal why the paradoxical effect occurs. However, one possibility proposed by Betsch and Sachse is that an extreme statement of no risk is more attention-grabbing, which only serves to highlight the possibility that risk is an issue. Another potential explanation is that people look for ways to combat claims they disagree with, and if those claims are stated more strongly then that encourages people to marshal even stronger counter-claims of their own.

The results have obvious implications for real-life risk communication. "Especially when organisations lack complete knowledge about how much trust the public puts in them, optimal risk negation is likely to profit from moderate rather than extreme formulations," the researchers said.
Betsch, C., and Sachse, K. (2012). Debunking Vaccination Myths: Strong Risk Negations Can Increase Perceived Vaccination Risks. Health Psychology DOI: 10.1037/a0027387

Previously on the Research Digest:
How to promote the MMR vaccine.
The psychological barriers facing MMR promotion campaigns.

Post written by Christian Jarrett for the BPS Research Digest.


MDH said...

This is very interesting and intuitively expected results. Were the respondents asked about their perceptions of trustworthiness and honesty of the source? Were they asked whether the claims were believable? There seems to be quite a bit of evidence from advertising research (according to for example) that: two-sided ads are more believed than than one-sided ads, moderate claims are believed more than extreme claims, and that familiar statements are believed more than unfamiliar statements. The latter especially is a well known effect, and well used by propagandists as well as commercial advertisers. If we assume that most people are aware of SOME side effects to vaccines, then a statement that completely denies any would be less credible than one that accepted some, and harder to assimilate.

Alison Cummins said...

"No evidence" is not a strong statement, it's a weak one. It could as easily refer to the condition "nobody's ever bothered to check" as "we've looked really nard and there's nothing there."

"Weak evidence" includes the information that we have bothered to look. It's a more complete statement, and gives people something to work with.

Anonymous said...

It's really quite a waste of time that they're studying people's reactions to information concerning vaccines. Why not throw your money towards a real study; vaccinated bs unvaccinated. Instead they're spending money and time to try and figure out how to provide information which will lead us to believe what they say....what the he'll is wrong with this world?

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