On 08/03/2011 21:12, Dave Liquorice wrote:

Pretty sure that some forms of lung disease only have one cause...


That's possibly true. But how do you prove it? Say 90% of all cases
are in people who smoked. And the other 10% are in people who have been
exposed to smoke (or asbestos). You can't really tell whether some of
the cases were associated with something else, because of the strong
smoke (or asbestos!) effect on the disease.

Andy