It's very difficult to do, because it's difficult to show that something was prevented. It's easy to show that something happened. To my knowledge, that's sort of the third rail of primary prevention research, to show that if I spend $10, I can save $100; and even if we can come up with that number, how long is it going to take to save the $100?
On January 29th, 2008. See this statement in context.