Jeff Bennett, March 2004

In 1998, a British medical journal published a statistical study linking childhood vaccinations to autism. This study led millions of people (especially in Great Britain, but also in the U.S. and elsewhere), to forego vaccinations for their children. Just a few weeks ago, 10 of the original 13 authors of the study published a retraction, saying they erred in their conclusions. Thus, according to these authors of the paper, there is no current evidence to support the idea that there is any link between vaccinations and autism.

Questions for class:

* Let's assume that the 10 authors who signed the retraction are correct -- the original paper was wrong, and there is no evidence for a link between vaccinations and autism. Do you think people who have foregone vaccinations in the past few years would have behaved differently if the original study had never been published? Why or why not? (Answer: clearly yes. Vaccinations prevent diseases that are sometimes deadly. Very few people would skip vaccinations if there were no side effects to worry about. The autism study suggested a serious side effect, and influenced the choice made by millions of people.)

* No one knows exactly how many people did not get vaccinations or how many children got sick as a result. But let's make some simple estimates. Suppose that 10 million children were not vaccinated, and that 1 in 10,000 became seriously ill or died as as result. How many children were affected? (Answer: this is a simple numerical problem. Answer is 1,000 children.)

* The original study was based on just 12 children with autism, and took place 8 years after they were vaccinated. The original conclusions were largely based on parent memories of when autism symptoms started, and their claims that the timing was closely linked to the time of the vaccinations. Should the conclusions have been considered strong in the first place? (Answer: clearly not. Even without a retraction, the original statistical evidence was very weak. Reference: have students study our guidelines for evaluating statistical claims, which you can find in Unit 5B of Using and Understanding Mathematics or Chapter 1 of Statistical Reasoning in
Everyday Life.)

* It's quite likely that most of the millions of people who did not get vaccinations because of this study have not heard of the retraction. Thus, their children will remain unvaccinated. Suppose you were a national health official, how would you seek to get the word out to these many parents? Do you think they will believe the
retraction? How would you explain the change in scientific perspective on this question? (Discussion points: it might be particularly interesting to discuss the difficulty of retracting front page news of any type...)

* Overall, do you think it was a mistake for a medical journal to publish the original study? Would the journal have been criticized for NOT publishing it? How should journals decide when the evidence is strong enough to warrant publication? (Discussion points: This is highly debatable, since it goes to the question of who should decide whether the evidence is strong enough to warrant publication. Could lead to an interesting discussion of the peer review process along with its benefits and potential pitfalls.)