Probability Scale

Definite
Almost certain
Highly probable
A good chance
Likely
Quite likely
Better than even
Probable
Possible
Improbable
Highly unlikely
Unlikely
Seldom
Impossible
Rare

0 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Mean
-1sd +1sd

http://www.medicine.ox.ac.uk/bandolier/booth/PDF/estimateprob.pdf