Recently my co-blogger David Gorski wrote an excellent analysis of the latest propaganda effort from the anti-vaccine crowd – a website that attempts to deconstruct the fourteen studies most often cited to argue for a lack of association between vaccines and autism. As David pointed out, there are many more than 14 studies which demonstrate this, and no credible studies showing that there is any correlation. David covered some of the 14 discussed studies, and today I will discuss one more.

On that anti-vaccine propaganda site J.B. Handley begins his introduction with this logical fallacy:

Of all the remarkable frauds that will one day surround the autism epidemic, perhaps one of the most galling is the simple statement that the “science has spoken” and “vaccines don’t cause autism.” Anytime a public health official or other talking head states this, you can be assured that one of two things is true: they have never read the studies they are talking about, or they are lying through their teeth.

Of course this is  a false dichotomy, or forced choice.  I personally know of many people, including myself and David, who have both read all the studies and are telling the truth about our opinions that they do not support a link between autism and vaccines. It seems to be inconceivable to Mr. Handley that an informed professional could honestly disagree with his opinions – such is the nature of fanaticism.

It is also remarkable that Handley himself quotes many professional, expert, and advisory bodies who also have read the studies and concluded that they overwhelmingly support the conclusion of a lack of correlation between vaccines and autism – including the Centers for Disease Control, the American Academy of Pediatrics, The American Medical Association, the Institute of Medicine, and the March of Dimes. Handley casually and self-servingly assumes that all of the professionals in these organizations are incompetent or they are lying.

And keep in mind what it would mean to lie on this issue – Handley believes that many doctors who have chosen the career path of public health are deliberately condemning millions of children to autism simply to avoid admitting past error, because they cannot face the horrible truth, or to receive their Big Pharma kickbacks. It’s no wonder their rhetoric often becomes hysterical – they really believe this is going on. For some reason it is easier for them to believe this astounding horrible claim than even consider the possibility that perhaps they have misinterpreted the science and that trained experts who have dedicated their lives to understanding the science may know better. This is what we call the “arrogance of ignorance.”

I wish to add that there are also many scientist and physician bloggers who have also taken the time to analyze the data and agree with the consensus opinion of no link. We have no dog in this hunt. David and I, for example, do not prescribe vaccines in our practice, we do not work for pharmaceutical companies, we are not involved in litigation – we have none of the conflicts of interest typically cited to discredit otherwise valid studies or opinions. Our only personal stake in this issue, as science bloggers, is our reputations, which are based upon honest and transparent analysis. We have nothing to gain and everything to lose if we are dishonest or sloppy on this issue.

You also cannot legitimately argue, as many often attempt to, that we are just protecting the status quo or that we are doing this as a favor to our colleagues. We have taken up the task of criticising our colleagues and the status quo whenever we feel it is appropriate. We are in the business of ruffling feathers. Our only stake is in defending something we firmly believe in – science-based medicine.

But the anti-vaccine fanatics simply assume we must be hiding some conflict of interest, or that we are simply incapable of seeing the Truth. That is the paranoid behavior of a cult.

With David’s post for background on the methods used, I will add to his analysis one more of the studies in question.

Madsen 2003 Danish Study

Madsen et al evaluated autism rates in Denmark from 1971 – 2000. From 1961 – 1970 children received 400 micrograms of thimerosal. From 1971-1992 they received 250 micrograms of thimerosal. After 1992 all thimerosal was removed from childhood vaccines in Denmark. The study identified 962 children with autism over this period. They found that from 1970 to 1990 there was no change in the incidence of autism. After 1990 autism rates began to increase, which was attributed to expanding diagnosis and surveillance. These numbers generally match the experience in other Western nations.

The authors conclude that there was no association in their study between thimerosal dose and autism rates.  This is the same as the experience so far in the US – thimerosal was removed by 2002 and yet autism rates continued to rise without a blip.

The “fourteen studies” site gives this study a score of 1 on their rigged scale. There main criticism is that in 1994 outpatient records were used in addition to inpatient records to assess autism incidence. By itself this is a legitimate criticism, but it does no invalidate the study as they suggest. This is a potential weakness of retrospective studies – researchers are somewhat dependent on the consistency of methods used over the years in study. The authors of this study were completely up front about the changing methods over time and the potential impact on their data.

But anti-vaccine critics miss a couple of very important points. First, if thimerosal were a significant contributor to autism rates then we would expect (as with all toxins) a dose response effect. In 1970 the dose of thimerosal in the Danish vaccine schedule was reduced from 400 to 250 micrograms. This did not result in a decrease in autism rates 3-7 years later as one would predict from the thimerosal hypothesis. Autism rates were stable during this time, and there are no concerns about altering methods of diagnosis or counting during this time.

Second – Madsen and his co-authors were well aware of the effects of altering counting methods in their study. Therefore they did the following:

In additional analyses we examined data using inpatients only. This was done to elucidate the contribution of the outpatient registration to the change in incidence. The same trend with an increase in the incidence rates from 1990 until the end of the study period was see.

So they did a reasonable assessment of the effect of adding outpatient to inpatient records on their data by looking at the inpatient data alone, and they found the same trend.  This completely invalidates the criticism of this study by the anti-vaccine crowd, which is premised on the fact that the increasing rates of autism after 1990 were due to the addition of outpatient records.

The bottom line is that this study shows no correlation between changing doses of thimerosal and autism rates. It does reveal an increase in autism rates beginning in the early 1990s resulting from expanded diagnosis and surveillance. It is interesting that the anti-vaccine critics use that very fact to argue that this study is not valid. Yet otherwise they deny that increasing autism rates are due to these factors because it is their claim that the increase in autism rates were due to vaccines. They therefore directly contradict themselves.

In addition to a lack of correlation between thimerosal and autism, this study supports the conclusion that the rise of autism rates in the 1990s and beyond are due to changes in the definition of autism and efforts to make the diagnosis in the population. That is the common element between Denmark and the US. Exposure to thimerosal and the vaccine schedule differed between these two countries, and yet autism rates were similar. Thimerosal and vaccines are not the common element in the rise of autism diagnoses – definition and surveillance are. So this data becomes much more powerful evidence against a link between autism and vaccines when it is considered in the context of US data.

The “fourteen studies” website declares:

Where is the truth? Like everything else in life, the devil is in the details.

It is indeed.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.