Here’s a classic science communication fiasco. Many of us believe empiricism enables the resolution of uncertainty with data, and that more information is better than less. That’s why we do science.

One of the moral imperatives that drive us is that carefully scrutinized, systematically replicable, and objectively verifiable information trumps hearsay. It allows us to dispel rumour and prejudice by offering tangible evidence as the alternative. It may be a slow process, but gradually we crawl towards enlightenment. And so we become a better species.

A classic illustration of the reasons why is vaccination. Scaremongers who spread misinformation about vaccination — such as the vastly researched and now thoroughly debunked claim that MMR vaccination causes autism — can be refuted simply by presenting the contrary facts, backed up with data. Right?

Well, as it turns out, wrong.

Researchers in the US and UK presented 1,751 American parents with “corrective information” debunking MMR-autism claims, and found that it actually led to a 48% reduction in the extent to which parents then agreed with the statement

If you had another child, how likely is it that you would give that child the measles, mumps, and rubella vaccine, which is known as the MMR vaccine?

To repeat, this was AFTER receiving information correcting antivaxxer misperceptions, using language drawn from this website hosted by the US Center for Disease Control. The CDC website unequivocally states that

Vaccine safety experts, including experts at CDC and the American Academy of Pediatrics (AAP), agree that MMR vaccine is not responsible for recent increases in the number of children with autism. In 2004, a report by the Institute of Medicine (IOM) concluded that there is no link between autism and MMR vaccine, and that there is no link between autism and vaccines that contain thimerosal as a preservative.

The website goes on to list details of a number of “carefully performed scientific studies [that] have found no link between MMR vaccine and autism” :

A September 2008 case-control study published in Public Library of Science (PLoS) was conducted in 2004-2008 to determine whether results from an earlier study that claimed to find measles virus RNA in the intestinal tissue of a specific group of autistic children could be confirmed. The results could not be confirmed, and no link between MMR and autism was found.

An April 2006 study conducted by the National Institute of Child Health and Human Development (NICHD) of NIH and the CDC assessed data from 351 children with autism spectrum disorders and 31 typically-developing children. The study did not find a link between MMR vaccination and autism. The results were published in the Journal of Autism and Developmental Disorders.

A February 2004 case-control study examined the possible relationship between exposure to the MMR vaccine and autism in Atlanta, Georgia. The results were published in Pediatrics.

A November 2002 study by CDC and the Danish Medical Research Council that followed more than 500,000 children over 7 years and found no association between MMR vaccination and autism. The results were published in the New England Journal of Medicine.

When such information was shown to the 678 parents with “least” favourable attitudes to vaccines to begin with, their attitudes deteriorated worse than everyone else’s. Their willingness to have a future child vaccinated dropped to just 36% of what it was BEFORE they saw the corrective info.

So the lessons are: (a) showing people evidence that MMR doesn’t cause autism makes them more likely not to believe you; and (b) showing people who already don’t believe you makes them even less likely to do so.

The researchers suggest that all this is actually good news, because the findings help give researchers “the tools to learn more about what messages do work.” That’s a bit like saying that discovering your lover is cheating on you helps give you the tools to learn how to seduce them properly.

People, eh?