Anti-Vaccination Claims

July 17, 2009 at 10:24 pm (Alternative Medicine, Anti-Vaccination, Chiropractic) (, )

While reading a blog post written by a chiropractor bloke who is definitely not a chiropractor*, I noticed a claim that had been made regarding the vaccination status of children with whooping cough.

This claim was that vaccination could not be guaranteed to be 100% effective. This is true. However, the claim that “85.9% of children with whooping cough (pertussis) were fully immunised” was then made without giving readers any clue as to how this should be interpreted. What does it mean to say that the majority of children with whooping cough had been vaccinated against the disease? Well, it’s important to bear in mind that if the majority of children are vaccinated against whooping cough then it could easily be the case that the majority of those diagnosed have been vaccinated. This would not in itself say anything particularly meaningful about whooping cough or the pertussis vaccination. Are children who have been immunised more or less likely to be diagnosed with pertussis than those who have not? Does either group suffer from more or less severe complications? These are the sort of questions I’d be interested in finding out the answers to. I would not be particularly interested in learning simply how many of the children with whooping cough have been vaccinated, as it would not really mean anything to me on its own. This number alone would not inform me.

Let’s get hypothetical and pluck some numbers out of the air. If you have 1,000,000 children and 95% are vaccinated, then 950,000 children have some protection against pertussis, while 50,000 are left unprotected. Say 100 children catch pertussis. Of these children with pertussis, 86% are vaccinated and only 14% are unvaccinated. These figures might, at first glance, make it seem as if vaccination is pretty much useless – just look at how many vaccinated children got sick. However… of the 50,000 children who are unvaccinated, 0.028% have got whooping cough. Of the 950,000 children who were vaccinated 0.009 have got whooping cough. Using these hypothetical figures, we can see that it is easily possible for the rate of infection with whooping cough in the unvaccinated to be three times that in the vaccinated despite the potentially misleading figure that shows 86% of children with whooping cough had been vaccinated and may make us doubt the effectiveness of the vaccine.

In the comments section on the chirolive blog, someone asks the following question of the author:

Could you explain how the 85.9% figure relates to your argument and why you feel the percentage of children with whooping cough who are vaccinated is the best way to represent the data.

I think this is an excellent comment and the author doesn’t yet seem to have given a direct answer to the twin question that has been posed here. When people use numbers without giving any kind of context or explaining how the number supports their argument then you have to ask yourself how meaningful that statistic is. After all, I could claim that the majority of children who test negative for whooping cough have been vaccinated against pertussis – it’s a whopping 97.2% in the BMJ study** that is linked to on the chirolive blog – but on its own, taken out of context, would that figure really be meaningful? Would it tell us anything useful?

EDITS

*I have amended this post to make clear that the author of the Chiropractic Live blog is not actually a chiropractor. He does, though, still practise chiropractic. According to his blog: “I still practise chiropractic and am a passionate advocate of chiropractic.” (June 11th 2009). So he practises chiropractic, but is not a chiropractor. I’m pleased to have been able to clarify that for you.

**The PDF is available via this link. The abstract is here. While I did make clear that the BMJ study had been linked to on the chirolive blog, I failed to provide a direct link myself. I apologise for this uncharacteristic omission. Backup copy: whooping cough.

These edits were prompted by criticism from the chiropractor bloke who is definitely not a chiropractor, but who practises chiropractic in this blog post. I don’t feel that he has adequately addressed my criticism of his use of a single statistic, but you can judge this for yourselves should you wish to do so. If you do read his blog post for yourself it will at least mean that you do not have to rely on my biased interpretation of his writings. After all, I may have “a bee in my bonnet”.

Forthcoming blog posts

I’m writing something on the weapons of influence that may be useful to advocates of alternative medicine (I may be being a trifle ambitious in attempting to marry Cialdini’s work on influence and persuasion with Holford, McKeith and homeopaths, but we’ll soon see).

I’m also part way through a rant about psychics/mediums giving advice to people on how to live their lives.

9 Comments

  1. Another sceptic (jdc325s weblog) is not happy with my “scientific evidence” questioning their beliefs. : Chiropracticlive.com said,

    […] Anti-Vaccination Claims […]

  2. Neuroskeptic said,

    This is a textbook example of a statistical fallacy – quite literally. if I ever write a stats textbook, just before I die of self-loathing, I will include this as an example.

  3. Becky Fisseux said,

    This is quite a common twisting of stats by the JABS crew. I had a bit of a rant about an example from that proven liar Hilary Butler a while ago.
    http://tinyurl.com/vaccinelie

  4. jdc325 said,

    @Becky: yes, having visited your page and seen the example in your post it seems strikingly similar. Showing the motrality rates, but not the incidence rate is another trick I’ve seen before on JABS and I notice you have an example of that too.

    @Neuroskeptic: I’ve read How To Lie With Statistics and The Tiger That Isn’t and when I saw the lone percentage it sort of “rang a bell”. I must have read something that warned me about tricksy use of a single number out of context.

    ETA: I’ve just seen the comments on the chirolive thread. I see that Nico Mendes seems to be incoherently criticising my next blog post (apparently I am “going to go and try to extrapolate something used against homeopaths against all the practitioners of,what is it they like to call it? Woo or quackery”). I think he’s got the wrong end of at least one stick there. I’m not going to be “extrapolating something used against homeopaths”, I’m going to be looking at what “social jujitsu” hpaths and other altmed advocates use in order to persuade people.

  5. mmackay40 said,

    A recently released medical study might shed some light on this issue. I don’t know how to format comments, but here is the Title and Catchline of one of the many webpages about it:

    “Unvaccinated children 23 times more likely to get infected with whooping cough

    “26. May 2009 01:23

    “Children of parents who refuse vaccines are 23 times more likely to get whooping cough compared to fully immunized children, according to a new study led by a vaccine research team at Kaiser Permanente Colorado’s Institute for Health Research.

    “The study will appear in the June 2009 issue of the journal Pediatrics, the journal of the American Academy of Pediatrics.”

    Here is the url of that website:

    http://www.news-medical.net/news/2009/05/26/Unvaccinated-children-23-times-more-likely-to-get-infected-with-whooping-cough.aspx

  6. Andy said,

    Questions/thoughts off the top of my head:

    This was not a trial aimed at comparing vaxed and unvaxed kids.

    The data is selected from patients who “presented to a GP” – in Oxfordshire. Good enough, perhaps, for the thing they were looking for (general advice on diagnosis) but unlikely to be useful for comparing vaxed and unvaxed statistics.

    How many of the initial 172 kids were unvaxed?

    Only 64 kids had whooping cough – not a particularly large sample to start deriving further data from.

    How many kids in Oxfordshire were vaccinated – ie. what percentage of vaccinated kids were represented in the 64 who presented in this study?

    How many kids in Oxfordshire were UN-vaccinated – ie. what percentage of UN-vaccinated kids were represented in the 64 who presented in this study?

    Were the symptoms and complications, if any, identical, better or worse, in vaxed and unvaxed sufferers (again, I doubt such comparisons are useful when this was not the purpose of the trial)?

    It’s 1am here but I just found the extended data here.

    One comment which refutes Richard’s claim of his family’s “lifelong immunity” due to natural infection…

    Despite data showing that neither infection nor immunisation results in lifelong immunity

    Oh, and here’s another quote before I go to bed…

    Most of the children in our study had received a full set of primary immunisations. Although immunisation failed to protect them against pertussis, it did result in attenuated clinical features.

    And…

    Our research suggests that in the United Kingdom pertussis is also endemic among younger school age children. This finding is important because secondary attack rates of pertussis in non-immunised household contacts have been estimated to be 90%. Younger children are more likely than adolescents to have a newborn sibling to whom they could transmit the infection with potentially devastating consequences.

    Not as clear-cut as Richard portrayed it from the little bit of info in the abstract.

    Holfordwatch has already dealt with some of this here.

  7. Andy said,

    I should add that I am not schooled in reading scientific papers – of any kind so take nothing I say at face value. Check for yourselves.

  8. jdc325 said,

    @mmackay40: thanks. The study abstract is available on Pubmed here – http://www.ncbi.nlm.nih.gov/pubmed/19482753

    We identified 156 laboratory-confirmed pertussis cases and 595 matched controls. There were 18 (12%) pertussis vaccine refusers among the cases and 3 (0.5%) pertussis vaccine refusers among the controls.

    @andy: thanks for your comments. “This was not a trial aimed at comparing vaxed and unvaxed kids.” Yep – the way I read it, the study showed that doctors should be wary of ruling out pertussis infection merely because children have been vaccinated. It seemed to me that it was more about giving GPs a heads-up than an attempt to compare rates of pertussis infection in vaccinated and unvaccinated children.
    PS – I note that one of the questions I said I would be interested in asking when discussing pertussis infection in vaccinated and unvaccinated children (“Does either group suffer from more or less severe complications?”) is actually answered in a quote you used: “Although immunisation failed to protect them against pertussis, it did result in attenuated clinical features”.

  9. Measles in Pakistan: Anti-Vaccine Websites Go Cherry-picking | Stuff And Nonsense said,

    […] also neglect to tell readers what vaccine coverage is (a piece of information that is necessary for anybody wishing to make a comparison between vaccinated and unvaccinated children for rates of […]

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