Along these lines, the Kelly Criterion is not necessarily applicable trading because, contrary to what Kelly presented (p925) in his paper, it does not yield the optimal "fr action" to risk, but rather, a risk factor. That's ok, provided you understand that going in -- if not, you will be likely wildly overly-aggressive. The Optimal f formula DOES provide the optimal fraction.
It's possible to translate between the two, just as one might translate between Fahrenheit and Celsius. There is an enormous benefit to using the optimal fraction, however, as it is possible from that to determine what the best guess for the future value for f (as a fraction) will be.
I won't elaborate further on that, but if you;re interested this is detailed in the forthcoming Journal of the International Federation of Technical Analysts, presented in Berlin next month, or in Tampa in November (see ralphvince.com for more on this) -Ralph Vince