Thursday, July 10, 2008

Does Tylenol + MMR Cause Autism? Really?

Apparently a group at UC San Diego thinks so. Kristina Chew's blog, AutismVox, tipped me off about this in a posting today. The abstract for the article can be found here1. The text of it follows:
The present study was performed to determine whether acetaminophen (paracetamol) use after the measles-mumps-rubella vaccination could be associated with autistic disorder. This case-control study used the results of an online parental survey conducted from 16 July 2005 to 30 January 2006, consisting of 83 children with autistic disorder and 80 control children. Acetaminophen use after measles-mumps-rubella vaccination was significantly associated with autistic disorder when considering children 5 years of age or less (OR 6.11, 95% CI 1.42—26.3), after limiting cases to children with regression in development (OR 3.97, 95% CI 1.11—14.3), and when considering only children who had post-vaccination sequelae (OR 8.23, 95% CI 1.56—43.3), adjusting for age, gender, mother's ethnicity, and the presence of illness concurrent with measles-mumps-rubella vaccination. Ibuprofen use after measles-mumps-rubella vaccination was not associated with autistic disorder. This preliminary study found that acetaminophen use after measles-mumps-rubella vaccination was associated with autistic disorder.

Let us try to break this down:

  • The study was performed to determine if acetaminophen, taken after the Measles Mumps Rubella (MMR) vaccination is associated with autism spectrum disorder.

  • The data were collected via an online survey of parents over the course of about six months (16 July 2005 to 30 January 2006).

  • The samples were 83 autistic children and 80 control children.

  • This survey found that acetaminophen use after the MMR vaccination was significantly associated with autistic disorder in children under the age of five.

The first alarm bell that went off in my head was the use of an online survey to collect the data. The abstract does not reveal how the survey was presented to the parents, whether the parents selected themselves to participate in the survey, or even where the surveys were conducted. I probably will not find out, since the publishers of the journal Autism allow only subscribers to view the article.2

Childhood vaccination has become a political and emotional issue these days, and there is no doubt that some parents have strong opinions about it. I would think it remarkable to expect parents to put aside their biases and emotions and then fill out survey form in a dispassionate manner.

Next, how were these children chosen? Did the authors post something on a website seeking test subjects? How did they screen for suitable subjects? Did they actually examine the children at any point, or did they simply rely on the parents' word? Can a parent's memory, already pretty biased, be relied on for data on when and how much acetaminophen was administered?

The sample sizes are also suspicious. If we accept the statistic that 6 out of 1000 people are on the Autism Spectrum, why then did they only sample 80 children for their control group? A real control group ought to be much larger.

My thoughts on this are that the researchers were doing a lot of hand-waving and were pretending to be performing a double-blind study. I am very much reminded of Feynman's dismissal of "cargo-cult" science, in which people will use scientific terms and methods in a slipshod manner in order to make their research look "respectable".


  1. S.T. Schultz, H.S. Klonoff-Cohen, D.L. Wingard, N.A. Akshoomoff, C.A. Macera, Ming Ji, "Acetaminophen (paracetamol) use, measles-mumps-rubella vaccination, and autistic disorder", Autism, Vol. 12, No. 3, 293-307 (2008) DOI: 10.1177/1362361307089518

  2. This is another one of the high horses that I sometimes ride: the practice by academic journals of restricting access to their articles. Considering that the vast majority of the research that the articles are based on are paid for with taxpayer money, and that the journals rely on what is essentially free labor by both the authors and the peer reviewers, it strikes me as unjust for these journals to then demand great sums of money to access these articles. This is, however, a subject for a later post.

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