I've always thought of it as A. for scalps ( small ROI with zero risk ) and B. on middles ( potentially large profit margin when compared to actual risk if you can get a -2'/+3' ). ROI is not really how I evaluate/look at middles because scalps have no "gamble" in them whereas middles do - barring any "lead" considerations. So I see the "moved $" as important to the scalp ROI and the ROI is always positive on each attempt. But not so for the middle since there is risk and a particular middle is highly likely to have negative ROI but there is +EV long term and a long term profit expectation. But I am no expert and that is just the way I look at it. Mach's example is a combination "almost" scalp ( 0 cent ) and side, so it is a bit of a grey area, admittedly.
cz,
I'd calculate the 57% as:
.57*2 - (.43 * 2.2)= .194 which is a little under 4 times the middle ratio you calculated, not sure where you got .97 but it is only fair to compare the same 2.2 units bet between the scenarios! I do look at middles like B., so 50% vs 19.4% is my comparison.
I'd think because the actual risk on a middle is .1/2.2 vs 2.2/2.2 on a straight bet you'd want to bet more UNITS per middle attempt ( or a bigger % of bankroll ) than you would on straight bets. I know that mine tend to be 10-40 times as big as my straight bets but I don't use Kelly so I don't know what it would dictate! I also VERY RARELY have .1/2.2 at risk, usually much less and correspondingly less than a 10% hit expectation on a clean middle!
JMHO  |