I don't remember having a concrete number in my mind. I guess I'd assume .1% for today. Had a picture of it as "something that's very tragic and basically doesn't happen anymore". While .5% puts it into the "not likely but might happen to you" range.

And as for a century and two ago I'd be waaaaaaay off base. Probably 10% or even 5%. It's hard to say in the hindsight. Now it seems so obvious and makes you feel stupid.