Out of 400 possible results the Rogue can win 235 ways, draw 20 ways and lose 145. These all have equal weighting.
Success: 58.75%
Draw: 5.00%
Failure: 36.25%
Edit: When the rogue is the underdog in a contest the advantage is worth less than that, but when the rogue is the favourite the advatage is worth more than those numbers.