I wrote about this classic crank gambit a bit about a week and a half ago, emphasizing that no amount of studies will convince a crank.
Now, MarkH at denialism.com takes on the same issue in more detail so that I don't have to bother with David Kirby's latest spew. Thanks, MarkH! The point is that, for people who've already made up their mind to take a position that already contradicts what large amounts of available evidence says, no amount of other studies is ever enough. The "just another study" gambit should be recognized for what it is: a delaying tactic designed to buy time and distract people from the already existing scientific evidence against the crank position. It's a shifting of the goalposts.
Your welcome. it's already attracted a troll I thought I had dispensed with. His wit and wisdom seems to be to call the expert witnesses for the government in the autism omnibus "whores" with the usual failure to address any criticism.