They estimate a variety of of conditional statements ("AI possible this century", "if AI then FOOM", "if FOOM then DOOM", etc...) with magnitudes between 20% and 80% (I had the figures somewhere, but can't find them). I think when it was all multiplied out it was in the 10-20% range.

And I didn't say they thought other things were more worrying; just that AI wasn't the single overwhelming risk/reward factor that SIAI (and me) believe it to be.