This thread might be relevant.

I am actually interested in studying game balancing, if by any chance you have documents related to this, please give me the links ;)

I haven't read the series yet, but the Game Balance Concept series (10 articles) might be interesting:

This TV Tropes page is also nice. And here's some of my own thoughts.

Thanks for the link you posted!

@Servant of the Lord,

Thanks for the links.

I had found Ian's blog already, I will read the 3 others links carefully. :)