A great post on Advocacy Research from A Photon in the Darkness - How to Seek and Not Find (March 31, 2006).
A very abridged version I give here, so go and read the whole post (which includes links etc):
Dan Olmsted, UPI's Senior Editor for autism-mercury conspiracy... He even performed an "exhaustive" search of the Lancaster County Amish communities looking for autistic children. His failure to find any (other than children who had been vaccinated) is further evidence - he claims - that ...the thimerosal in vaccines is responsible for causing autism.
But, as pointed out at Photon in the Darkness there is:
…another possible explanation ...a group of researchers from the Clinic for Special Children in Strasburg, Pennsylvania ...report a genetic mutation which causes:"...seizures that progress to autism and retardation" …However, it seems passing strange that Mr. Olmsted, in his extensive canvassing of the Lancaster County Amish communities, did not run across a few of these children. They are, after all, autistic, even if they weren't vaccinated.
Three possibilities leap to mind (there may be others):
[a] Mr. Olmsted didn’t look all that carefully for autistic children, having already concluded that there wouldn't be any.
[b] Mr. Olmsted found these autistic children, but didn't count them - either because he (as a trained neurologist and developmental pediatrician) didn't feel that they had real autism or because it conflicted with his forgone conclusion.
[c] The Amish families - being somewhat suspicious of "outsiders" (not without good reason) - didn't confide the details of their family medical issues with Mr. Olmsted.
My money is on [a], with a bit of [c] thrown in for good measure.
One thing my thesis advisor [sic] told me early in my education:
"If you don't look for contradictory data, you won't find it. But your critics will."
Technorati Tagged - Fallacy, Science, Skepticism.