Unfortunately, the numbers mean very little. Here's my take on it.
Your chances of being published without an agent= slim
You chances of being published with an agent= better
Really, though, even if you ahve an agent with a 99% placemen rate for first-time authors, if you are that one percent, the other 99 doesn't make you feel much better, does it.
The fact of the matter is you will dramaticallyincrease your chances of being
well-published if you have an agent to advocate foryou.
There is also the argument that the "better" agent you have, the more likely you are to be published, but that is a whole different ballgame.
Don't let stats get you down, just remember that what most of us are trying to do is not guarantee ourselves publication, but to give ourselves and our books the best chance possible. That's what an agent does.
Maprilynne