On 5/5/2011 6:15 PM, Tom Lake wrote:

It's not a "fault" of the study any more than an inability to fly is a
fault of a tractor. It's simply a property of that type of study; you
start with existing data and study them. I'd bet half of the studies
published on any topic use post facto data. I think you'll find that
*all* helmet studies are thus. That doesn't make them flawed; they
have their limitations; however, they're the best we've got or ever
will have. It's a stronger design than a whole-pop because I can
scale the results; whole-pops only apply locally.

For vehicle crash-worthiness there are some tests that are designed to
simulate a real accident with the use of crash test dummies. But of
course what is also looked at is post facto data on accident data,
comparing the use and non-use of safety equipment by accident victims.

Be very careful about those people that misuse whole population studies
with claims that they are inconclusive because out extenuating factors,
because often those extenuating factors are things they made up out of
thin air. For example, there is absolutely _no_ evidence that cycling
rates fall after helmet laws are introduced, but that does not stop the
birther-like claims that the only reason that whole population studies
show a decrease in injuries and fatalities is that cycling rates went
down. Of course first they started out denying any decrease, then when
they couldn't deny it any longer they came up with a rationalization for
it. This is covered in Myth 8 at
http://sites.google.com/site/bicyclehelmetmythsandfacts/#TOC-Myth-8:-Studies-show-that-when-helm

Before the proliferation of web sites where actual scientific and
statistical data was available for all to see, Usenet had a lot more
"helmet wars." Now, with the data readily available, you see just how
furious people like Frank and Phil become when the facts don't agree
with their agenda. The "Bicycle Helmet Myths and Facts" web site that I
started as an effort to have a central repository for all the myths that
the AHZs try to put out there, and the actual facts, has been a big help
with reducing the helmet war threads.