Comment by tialaramex

Think of it as shared responsibility. The tobacco and the virus are both reasons why you got cancer and died, prizes for all.

So maybe 70% of throat cancer victims have HPV, and like 70% smoked - and if those were independent facts you'd expect that about 49% both smoked and had HPV, but it's actually more than half 'cos it turns out that if you have HPV then smoking is even worse. So that's nice.