Opinion Change – Judgement and Decision Making


An Examination of The Psychological Mechanisms Behind Why Parents Blame Vaccines For The Ill-Health of Their Children
November 2, 2010, 5:27 am
Filed under: Uncategorized

Immunization saves approximately 3 million lives each year (Australian Government Department of Health and Ageing, 2008). Despite this amazing achievement of science, there are many people who are against vaccination. However these anti-vaccination beliefs are not supported by scientific research. Why then, does vaccination get incorrectly blamed for health issues? This paper will give a brief overview of the common myths put forward by anti-vaccination lobbyists, and the scientific research that debunks them. However the focus of this paper will be on the psychological mechanisms behind the faulty beliefs that people hold that link vaccination with health issues.

There are many unsubstantiated claims put forward against vaccination, the following are but a few of the more common ones. One of the most popular anti-vaccination myths is that the Measles Mumps and Rubella (MMR) vaccine causes inflammatory bowel disease (IBD) and autism. However a review by the World Health Organization and also a separate review by the Institute of Medicine both concluded that current scientific data do not show any causal link between the MMR vaccine and autism or IBD. Another common myth is that the flu vaccine causes the flu. However this is impossible. None of the influenza vaccines used in Australia contain live viruses (Australian Government Department of Health and Ageing, 2008).

Yet another myth is that vaccines cause or spread the diseases they are supposed to prevent. However the majority of vaccines are inactivated or only partially prepared from the organism. Therefore the organism is not alive and it is impossible for it to cause disease. Exceptions are very rare. For example the risk of the first dose of the oral polio vaccine causing disease is one per 750,000. However even this rare occurrence is no longer an issue in Australia as it has been replaced by the inactivated polio vaccine (Australian Government Department of Health and Ageing, 2008).

With the vast majority of scientific data going against the arguments put forward by anti-vaccination lobbyists, why is it then that so many people still believe the myths? One of the major psychological mechanisms behind these faulty beliefs involves seeing patterns where there are none. Take for example this heart wrenching piece of anti-vaccination propaganda put forward by a member of the Think Twice anti-vaccination website:

“Harley had the sniffles and Ashlee had a cold, otherwise both were in perfect health. Harley was given his first DPT, polio, and Hib shots. Ashlee received her first Hib and MMR shots, as well as her third DPT and fourth polio shots…

For ten days Harley’s behavior changed. He barely slept, hardly ate, and seemed to be getting worse. On May 17 at 9:00 a.m., my husband got up, checked on Harley, and yelled out, ‘Bonnie, get up, call the ambulance. Harley is dead!’

The state police and county coroner arrived with the ambulance. The coroner peered into the ambulance, never examined Harley, and stated, ‘SIDS.’ Harley was then rushed away. My husband and I didn’t get to see him again for more than three days, until 1:00 p.m. on May 20 — in his coffin!”

It’s a sad and truly horrible story; the pain that the family experienced was tremendous. But is it right to conclude that it was the vaccines that caused this death? If you look at the situation with the emotional content removed, you see three things: (1) the child was already sick with the ‘sniffles’, (2) the child was given vaccines, (3) the child died 10 days later. From this information alone, we can either conclude that: (1) the ‘sniffles’ was something more sinister and caused the death, (2) the vaccines somehow caused the death, or (3) the child simply died from SIDS. The first conclusion was not even mentioned by the grieving parent, most likely due to the common nature of the sniffles amongst children. The second conclusion, that the vaccines were at fault, goes against the scientific data. In fact the most likely cause of the child’s death was SIDS.

As it turns out, if you take into consideration the vast number of cases of SIDS, by chance alone 2 children should die each year within 24 hours of receiving a vaccination (Australian Government Department of Health and Ageing, 2008). The above example involved a child dying not within 24 hours of receiving a vaccination, but within 240 hours of receiving a vaccination. Therefore the chances of their child simply dying from SIDS was even more likely. However these chance occurrences are not taken into consideration by the parents of a child who has died post-vaccination. Instead they see a pattern where the scientific data suggests that there isn’t one.

Another psychological reason, behind why parents blame vaccines for the ill-health of their children, is the errors associated with multiple endpoints. An endpoint is a possible outcome for a prediction. Specific predictions with only one possible outcome are much more impressive than a general prediction with a thousand possible outcomes (Gilovich, 1993). The likelihood of a child being vaccinated and within 24 hours dying due to SIDS is very low. However parents who blame vaccines for the ill-health of their children have many possible illnesses to attribute to the vaccines. There is no specific prediction amongst anti-vaccination lobbyists that vaccination will result in SIDS. In fact they predict that vaccination can result in anything from allergic reactions to autism. The World Health Organization (2010) has classified 12 420 diseases, many of which could coincidentally occur at the same time as a vaccination. The anti-vaccination lobbyists have such an incredibly general prediction of ill-health due to vaccination, that there is literally thousands and thousands of possible endpoints. Therefore it is highly likely that a child will fall ill, to any one of the thousands of possible illness in the world, at the same time as their vaccination and for the parent to wrongly conclude “aha! I knew it; I knew vaccinations would make my child sick!”

This coincidental occurrence of vaccination and illness is made even more likely when considering the fact that a child receiving all of the vaccinations recommended for them, will have received 16 vaccinations by the age of 2 (Illinois Department of Public Health, n.d). Sixteen times the chance is given for one of 12,420 illnesses to occur at the same time as a vaccination. Anti-vaccination lobbyists do not predict that the illness will occur on the first vaccination, or the second, or the third, they simply predict that an illness will occur at the same time as a vaccination. Therefore if any illness can occur at any vaccination, there are 198,720 possible end points in the prediction that vaccination will result in illness. There are approximately 500,000 children under the age of 2 in Australia and the prediction that vaccines make children sick, only needs one instance of illness amongst all those children to be paired with a vaccination (Australian Bureau of Statistics, 2007). That means that if all those children get their recommended vaccinations, there are 500,000 children multiplied by 16 vaccinations, multiplied by 12,420 possible illnesses, resulting in 99,360,000,000 possible end points for the prediction that vaccines will make children ill.

Seemingly-fulfilled prophecies also explain why some parents may blame vaccines for the ill-health of their children (Gilovich, 1993). Take for example the case mentioned previously, a mother got her children vaccinated and then subsequently the child died. With the mother blaming the vaccines for the death of her child, there is no way she will ever let any of her other children ever get vaccinated again. This means that her personal prophecy, that vaccines will make her children ill, stops her from ever giving vaccines another chance to prove her prophecy wrong.

The availability heuristic further explains why parents blame vaccines for the ill-health of their children. The availability heuristic refers to a cognitive bias where people report the frequency of an event based on how easily an example can be brought to mind. The same error that Lichtenstein, et al (1978) discovered, when people judged that it was more likely for them to die from the rare occurrence of homicide as opposed to the common occurrence of stomach cancer, is present with parents judging the likelihood of their child falling ill due to vaccination. It is incredibly rare that a child will have an adverse reaction to a vaccination, but those rare cases are widely reported by the media, much like homicide. However the extremely common cases of children being vaccinated and being perfectly fine, are not widely reported in the media, much like stomach cancer. Due to this availability in the media, parents can more readily recall instances of illness as a result of vaccines. This results in a cognitive bias where parents believe that illness as a result of vaccines is much more common than it actually is.

The false consensus effect may be yet another psychological mechanism at play when parents blame vaccines for the ill-health of their children. The false consensus effect refers to when people overestimate how much their own beliefs, values, and habits are shared by others (Gilovich, 1993). This effect comes about because we are selectively exposed to certain information in our social life.  A cause of this, which relates directly with beliefs about vaccinations, is inadequate feedback from others. Inadequate feedback arises from the social propensity of people to be polite and nice. For example if a mother introduces you to their child and the child has a ridiculous name, you are very unlikely to let the mother know your opinion. Even if the mother asked you what you thought of their child’s name, it is very unlikely that you will tell her just how ridiculous it is. The mother is therefore likely to believe in a false consensus regarding how good their child’s name is. This same effect may be occurring with parents who blame vaccines for the ill-health of their children. If a parent has a sick child in hospital and believes that vaccines were the cause of this illness, it is very unlikely for a friend to denounce the distraught parent’s views even if that friend believes the parent’s views are totally wrong. This parent will therefore develop a false consensus regarding the role of vaccines in their child’s illness. Furthermore parents, who blame vaccines for the ill-health of their children, are most likely not going to be corrected by the people they tell. For example, if a mother is holding their child on the bus, and says to the person next to them ‘we don’t vaccinate our child because vaccines can cause autism’, it is unlikely that the person on the bus hearing this has any knowledge of the scientific data or lack thereof, behind this claim. Therefore it is unlikely for the person on the bus to correct the mother, and the mother’s false consensus regarding the role of vaccines in childhood illness will be reaffirmed.

So what impact are these beliefs having on children’s health? If you use the MMR vaccine as an example In England and Wales, the faulty beliefs surrounding this vaccine has resulted in only 75% of the population being vaccinated (Spooner, 2002). This has in turn resulted in a sharp spike in confirmed cases of measles, up to 1144 cases of measles in 2009 (Health Protection Agency, 2010). Now compare England and Wales’ 75% vaccination rate and 1144 cases of measles, with Canada’s 95% vaccination rate and 12 cases of measles (Spooner, 2002). It is abundantly clear that the detrimental effect of the faulty beliefs surrounding vaccines is resulting in lower vaccination rates and higher levels of disease.

We are now faced with the final problem; that information, about faulty cognitive processes regarding vaccines causing ill-health in children, will most likely be dismissed by those parents who hold such views. When faced with information, such as that presented in this report, parents can ask themselves one of two questions: “can I believe this” or “must I believe this”. The level of evidence required for affirmative answers to these questions is extremely different. Parents who are anti-vaccination have a bias that leads them to approach evidence opposing their views with the question “must I believe this?” However parents without this bias will most likely ask the question “can I believe this?” This therefore leads us to conclude that while anti-vaccination biases exist in the minds of parents, it is unlikely that any scientific evidence to the contrary, will be viewed as adequately convincing.

Reference List

Australian Government Department of Health and Ageing. (2008). Responding to arguments against immunization: A guide for providers. Australian Government.

Australian Social Trends. (2007). Retrieved October 7, 2010, from Australian Bureau of Statistics web site: http://www.abs.gov.au/AUSSTATS/abs@.nsf/0/04FEBEF9C 81FE6BACA2573 2C002077A2?opendocument

FAQ on ICD. (2010). Retrieved October 5, 2010, from World Health Organization web site: http://www.who.int/classifications/help/icdfaq/en/index.html

Gilovich, T. (1993). How we know what isn’t so: the fallibility of human reason in everyday life. New York: The Free Press.

Lichtenstein, S., Slovic, P., Fischhoff, B., Layman, M. and Combs, B. (1978). Judged frequency of lethal events. Journal of Experimental Psychology: Human Learning and Memory, 4, 551-578.

Parents Guide to Childhood Immunizations. (n.d). Retrieved October 7, 2010, from Illinois Immunization Program web site: http://www.idph.state.il.us/a bout/pgci.htm

Personal stories of vaccine damage and death. (n.d). Retrieved October 7, 2010, from Think Twice Global Vaccine Institute web site: http://www.thinktwice.com/stories.htm

Spooner, H. M. (2002). Measles outbreaks in UK linked to fears about MMR vaccine. Canadian Medical Association, 8, 166.

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2 Comments so far
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