Post Hoc Ergo Propter Hoc

As of 2008, 39% of parents refused to vaccinate their child compared to 22% in 2003. 25% of this group were worried the vaccines might cause autism. Unfortunately, statistics show a steady rise in this trend. If enough people refuse vaccines, then the disease could become prevalent again and society at risk of epidemics as these diseases reemerge.


The belief that vaccines may cause autism has been around for a little under two decades. In 1998, The Lancet published a study by British doctor, Andrew Wakefield. The study, titled "Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children", at first seems as indigestible as most other scientific journal articles. However, when you read into the abstract and manage to get past the bland, technical language, you might notice that he says, "Onset of behavioural symptoms was associated, by the parents, with measles, mumps, and rubella vaccination in eight of the 12 children..." In one sentence, Wakefield claims that the onset of autism begins after the children received the measles, mumps, and rubella (MMR) vaccine.


As you might imagine, this discovery added fuel to the anti-vaccination fire. If eight out of 12 children developed autism, generalizing those statistics would mean 66.7% of children would develop autism from one vaccine. HOLY CRAP?!... Right? If the Wakefield study were correct, then holy crap would definitely be an acceptable response to the findings. However, the Wakefield study has some very blatant errors that must be addressed.


First, let's look at the study itself. If you've learned a little about the scientific process, there are a few things that really stand out in the abstract. For instance, the quote "eight of the 12 children..." jumps out at me. Why are only 12 children involved in the study? If a scientist wants evidence that can be generalized across the population, he would choose a large and varied sample size from multiple populations. Then, even within the same sentence, he says, "behavioural symptoms was associated, by the parents, with" the MMR vaccine. The basis for his scientific analysis was that the parents believed they saw symptoms of autism after the vaccine? But maybe it was just an error or a call for more research?


Unfortunately, "Wakefield was being paid as an expert by lawyers who were suing over alleged vaccine injury. In fact some of the children in the study were the children of parents who were suing. This is a massive conflict of interest." This means that those errors weren't errors at all, but various forms of bias, making this whole debate totally irrelevant. The Lancet fully retracted the study after years of fighting to get it removed. Nonetheless, parents still refuse to get their children vaccinated based off of Wakefield's study.


The MMR vaccine is given to children twice. The first dose is given at 12-15 months of age and the second dose is given between four to six years old. According to the National Institute of Child Health and Human Development, most children display early signs of autism from 12-18 months. The overlap of time frames appears to be the root of the problem according to an interesting theory published by Livescience. The human population seems to be falling prey to a fallacy of logic that the Romans expressed with "post hoc ergo propter hoc" which means "after this, therefore because of it." Modern day psychology and statistics students put it differently, "Correlation is not necessarily causation."


This is meant to teach students to think past what may just be coincidence and try to find all possible reasons for the result (in this case autism). But, not everyone is a psychology student, so most people only see the correlated event (vaccinating against MMR) as the entire reason for the development of autism.


Since it is necessary to maintain herd immunity in the population, scientists and health officials are hard at work trying to regain public confidence. Many studies have been published that examine whether Wakefield could have been correct (none have found evidence for the autism theory) but there are still parents who believe vaccines cause autism. Feeling frustrated, scientists conducted a study meant to find out how people are responding to the methods they use to refute the anti-vaccination movement.


This study (published March 3rd, 2014) looked at 1,759 parents that believed the MMR vaccine causes autism. The researchers then tried to convince groups of parents to change their beliefs using four different methods: information on lack of evidence for the autism theory given by a health authority; information on measles, mumps, and rubella also given by a health official; pictures of infants who had measles, mumps, or rubella; or a story of an infant who almost died from measles. The study came up with some counter-intuitive results.


At the beginning of the study, 70% of parents were likely to vaccinate a future child against measles, mumps, and rubella. After the study, the group that had been given information refuting the vaccine-autism link were only 45% likely to vaccinate future children, although they no longer believed that autism was linked to vaccines. The participants were actually LESS likely to want to risk the vaccine even though they now knew that the autism debate was incorrect. This is a major problem because that is how scientists have been trying to dispel the misinformation for the past two decades.


A scientist's entire profession revolves around knowledge and how to look at it logically and refute what might be incorrect, but the scientific community doesn't seem to think the same way as most people. Using their normal methods, scientists seem mostly to be making people more stubborn and set in their ways. To convince people to vaccinate, they need to find new ways to appeal to people. No doubt there is more than one answer for how to increase vaccination rates. Even in just the comments of the study, there were ideas ranging from bringing back fear of the diseases to publicizing the personal and social side effects of the illnesses. It seems to me that a mixture of these ideas would have a greater effect. But first, we need to know what direction to head in.


So, in the words of Maester Aemon in A Dance with Dragons, “Knowledge is a Weapon, Jon. Arm yourself well before you ride forth to Battle.”


Sources:
http://www.scientificamerican.com/article/antivaccination-parents-dig-in-heels-even-after-receiving-medical-info/
http://www.livescience.com/2845-autism-vaccines-bad-logic-trumps-science.html
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(97)11096-0/abstract
http://www.sciencebasedmedicine.org/lancet-retracts-wakefield-article/
http://www.webmd.com/children/vaccines/news/20100505/more-parents-refuse-delay-childs-vaccination
http://www.cdc.gov/vaccines/hcp/vis/vis-statements/mmr.html
http://www.nichd.nih.gov/health/topics/autism/conditioninfo/Pages/symptoms-appear.aspx