Evaluating medical studies

Currently, the ScienceBlogs Book Club is discussing Paul Offit's Autism's False Prophets (which I've just ordered). For those unaware of the subject of autism and autism research, the heated discussion going on in the comments sector will probably surprise you.

The heat is because the debate about autism, and the cause of autism, as it happens on the internet, is not about science, but about emotions, and in some cases, about profit. When I say profit, I'm not referring to the pharmaceutical businesses, that makes the vaccinations, that some people claim causes autism, but rather the people pushing dangerous "cures" at high prices to the parents of autistic children. Because, frankly speaking, vaccinations are very low on the profit scale when it comes to the pharmaceutical sector (Viagra and happy pills would be a much better business).

Of course, just because one side might profit from something being true, doesn't mean that it's not true. The makers of penicillin make a profit, yet penicillin has saved more lives than it's possible to count.

When I first heard about the possibility of an autism-vaccination link, from a blogger I respect, I thought it sounded somewhat feasible, since the cause of autism is not particularly well known. Also, the fact that vaccinations contained thimerosal, which is based on a type of mercury, seemed worrisome.

In other words, while I wasn't convinced of the link, I certainly was open to the idea.

However, I began to run into other bloggers, pointing out the problems with this hypothesis, and I began noticing a problematic pattern. There has been a lot of research into autism, and a lot of research into the possibility of an autism-vaccination link. A few studies pointed towards an autism-vaccination link, while the majority showed no link. As such, this might not tell us one way or another, since the minority studies might be the better studies. However, by any objective measure, this was certainly not the case, and what's more, it turned out that, while we don't know everything about the cause of autism, we do know some things, and what we know, invalidates the hypothesis of a link between autism and vaccinations.

So, how does one go about evaluating studies? Well, I obviously have some criteria I follow, but instead of going through them, I think it's much better to point to an excellent article on the very subject in the NY Times by Gina Kolata: Searching for Clarity: A Primer on Medical Studies (might require that you log in).

Kolata explains clearly what kind of things you have to look at when evaluating medical studies, and while the examples she refers to, all had the minority studies overturn the majority studies, it's much more common the other way around, as we can see in the studies about autism-vaccination links.

For more stuff about the proper way to evaluate and do medical studies, I recommend the group-blog Science-Based Medicine.

Autism as mercury poisoning

Note: For many people, the following will be well known stuff. However, I feel that it's a good idea to repeat this information as often as possible, since there is still so much misinformation about the subject around.

In recent years there have been a group of people claiming that autism is not a neurological condition in its own right, but rather a result of mercury poisoning.
This idea is especially spread by anti-vaccination groups, where the poisoning is blamed upon the content of thimerosal in vaccinations.
A good example of this claim, is the article Autism: A Unique Type of Mercury Poisoning, which among other things claims:

A review of medical literature indicates that the characteristics of autism and of mercury poisoning (HgP) are strikingly similar.

The claim of a similarity between the characteristics of autism and mercury poisoning are similar, is quite doubtful. For one thing, the article focuses on the similarities in the most general of ways, and is very unspecific when it comes to describing the symptoms. It also ignores the very major differences between the symptoms of mercury poisoning and autism. As this commentary in Pediatrics explains:

Bernard et al1 present a table listing 95 clinical findings they consider to be shared by autism and mercury poisoning. Their table does not distinguish typical and characteristic manifestations of either disorder from the rare, unusual, and highly atypical.
In mercury poisoning, the characteristic motor findings are ataxia and dysarthria [..]. These signs, along with tremor, muscle pains, and weakness, are noted on relatively high-dose exposure, acute or chronic. In 3 Romanian children accidentally exposed to ethyl mercury in a fungicide, these same symptoms were prominent.7 The outcome of fetal methyl mercury poisoning in severe form also included spasticity.8 In contrast, in autism, the only common motor manifestations are repetitive behaviors (stereotypies) such as flapping, circling, or rocking. Persons with Asperger syndrome may be clumsy, and hypotonia has been noted in some infants with autism; the frequency of clumsiness and hypotonia in autism spectrum disorders is not established. No other motor findings are common in autism, and indeed the presence of ataxia or dysarthria in a child whose behavior has autistic features should lead to careful medical evaluation for an alternative or additional diagnosis.

There is even a handy table showing the differences.



Also, as the commentary points out, there is absolutely no evidence of a change in the number of autistics as the use of mercury changes. This is true for both the use of mercury (thimerosal) in vaccinations, and for the use of mercury in general.
When it comes to the use of thimerosal, there have been a number of peer-reviewed studies, conducted all over the world, looking at a thimerosal-autism link, and none of them have found any. It's possible to find problems with each of the studies, but taken together, the results are conclusive.

Also, a thimerosal-autism link doesn't explain why there is such a stalk gender-disparity. Mercury poisoning doesn't show the same kind of gender-disparity.

Having said all this, there are some pretty easy ways to make scientists take the mercury poisoning hypothesis more seriously. Simply make some credible research that shows that autistic children are found to contain whole blood mercury levels consistent with mercury poisoning. The current research into this, cannot be considered credible, and are indeed quite often found to be filled with flaws and errors.

Current research into autism shows that autism is most likely genetic in nature, and there have been research showing that autism can be linked to a part of chromosome 17, called 17q21. This is a promising path to better understanding of autism and its causes.

Many of the links in this post comes from Kevin Leitch's blog: Left Brain/Right Brain.

Note about comments: People are welcome to disagree with me and each other, but personal attacks will be deleted as soon as I see them. Spam linking to "mercury cures" and the like, will obviously also be deleted.