A Briffa's Wrong
The other day I posted about Dr John Briffa’s rant against p-values. He has since then posted some responses, in the form of several comments under the original post and a whole new rant. Er, I mean, blog entry, of course. Not “rant”!
His thesis remains much the same: no matter what anyone does, since science can’t prove a negative, we can’t be sure MMR doesn’t cause autism. Which is true, but of course can be applied to any stupid hypothesis you care to come up with. In his recent post, which is called “Why the MMR-autism ’˜war’ is far from over”, he says
What I am saying though is that there’s a huge pile of anecdotal evidence and some experimental evidence too which supports the idea that MMR vaccination might cause autism.
This really isn’t true. The Cochrane Collaboration examined 139 studies about MMR (not all about MMR-autism) and concluded that
No credible evidence of an involvement of MMR with either autism or Crohn's disease was found.
In any case, this always goes the same way. There’s a bad study done that “suggests” something, in this case that MMR might cause autism, and a load of people latch onto this for some personal reason, then when someone points out that the research is rubbish they deny it. Eventually the weight of evidence becomes so great that the course of least resistance is to drop that one tiny part of their stance: their position switches to “that study was bad, yes, we can see that, but our theory is still right”. If you ask them to show some non-bad research that supports their hypothesis then they’ll go and do a literature search vast (if not rigorous) enough to put any PhD student to shame, before coming up with some bizarre study about giving vaccinations to chimps or something, and I always look at those and think “hang on, where the fuck did that come from? You’ve been ranting about how bad MMR is for years, and this is the first time you’ve mentioned that study. In fact, you were ranting about MMR for years before it was published! How do you expect to convince me that that’s influenced your opinion in the slightest? I want to see the evidence on which you’ve based your opinions, if there is any.” Of course that doesn’t invalidate their chimp-based study, but it does show that they’re starting with a conclusion and then collecting evidence to support it, when they should be starting with evidence and basing the conclusion on that. Once you’ve established that, the last thing you should do is to criticise their evidence – it’s much quicker for them to find more shaky evidence than it is for you to dismantle it, so they’ll always be a couple of steps ahead if you let yourself get drawn into that fight.
The evidence used to persuade us of the safety with regard to autism is simply inadequate. The fact is, I don’t know whether MMR causes autism or not. But then again, it seems neither do those who insist it is safe.
He also says
Now, I’ve got a sneaking suspicion that those of the pro-vaccine lobby will want to claim that this blog is scaremongering by making out that MMR vaccination causes autism.
I agree with jdc about that quote.
And while the reason that the debate rages on is usually put down to the likes of Dr Wakefield and the parents who believe their children were damaged by MMR, the real guilty parties here have been our Governments whose intransigence regarding proper, definitive research in the area has inevitably left a huge question-mark hanging over MMR.
That’s plain wrong. As I said in his blog comments (assuming that he hasn’t deleted them, although he’s been good to jdc’s, so I don’t want to imply that he will), it would be unethical to do that study: if the study group was large enough to show the effect (which even anti-MMR types claim is very rare, even when they’re demanding that all three of their children were hit by it) then you’re deliberately avoiding giving a potentially life-saving vaccination to at least hundreds of children, on the basis that a few ill-informed, untrained, tabloid-reading morons think there might be a risk. There’s no way that would ever get past an ethics committee.
You have to be a little bit detached and just accept that the so-called link between MMR and autism is, in fact, just made up. That doesn’t prove it’s false, but it puts its odds at much the same level as other made-up hypotheses, such as ‘cider causes shortness’ or ‘MRI scans cause blindness’. (I just pulled those out of thin air.) Doing huge studies to attempt to disprove things you’ve made up would be a tremendous waste of time, and that doesn’t change just because they were made up a long time ago by someone else and then relentlessly repeated by bad journalists and angry but unqualified mothers.