I have been playing that game for a while now (mostly the wikipedia version), and I have the impression that the game is extremely imbalanced. In my circle of friend, the win ratio is about 80% for the spies. Is there any statistical data that gives a broader win ratio?
This thread provides the statistics you seem to be looking for, but with anything, correlation never implies causation. The OP came to the conclusion that your commenters did; the game is fairly balanced, and you really do need to assess the playstyle and strategies of your gaming group. Thing is, the best part of the Resistance is after the game itself is over.