Quote from caementarius:
You might look into the Kelly formula. Ernest P. Chan has a section on it in his book:
http://www.amazon.com/Quantitative-...bs_sr_1?ie=UTF8&s=books&qid=1230948282&sr=8-1
Free material:
http://www.tradingpatterns.com/Kelly.pdf
http://www.tradingpatterns.com/PositionSizing.pdf
The book is also excellent:
http://www.wiley.com/WileyCDA/WileyTitle/productCd-047022908X.html
Chapters 4 and 5 offer a good intro.
Ron