Relative Risk and Tort Law

Now here's a difficult problem -- mull it over and see what you think. A woman has been awarded $55 million in damages from Johnson & Johnson based on the claim that talcum powder caused her ovarian cancer.

Here's the 4-1-1 the actual relationship between talc and ovarian cancer. (I'm not sure if you can read it -- I have a magic cookie.) Summary:

Case control studies suggest that women who use talcum powder on their genitalia have about a 20%  increased risk of ovarian cancer, or maybe as much as 30%. That sounds pretty serious, but case control studies aren't conclusive about proving causation. Prospective cohort studies haven't confirmed this, but it would be nearly impossible for them to do so, because of what is called statistical power.

Ovarian cancer isn't all that common. In a 10 year follow-up period, 2 out of 1,000 women will be diagnosed with it. If the increased risk from talcum powder really is 20%, you would have to follow more than 100,000 exposed women and 100,000 unexposed women for 10 years in order to prove it. Put it another way -- the chances that an exposed woman will develop ovarian cancer attributable to talcum powder use is (2/1,000) * .2 = .0004, or 4/10,000.

Is the verdict justified? You decide.