Talon thanks for the input on the position sizing question. I put together a quick analysis of how both approaches fare in various vol regimes (using the system in this thread before filters), and the dynamic position sizing performed worse in nearly all scenarios. Now I should note that its far from conclusive at this point because it was only on the 5 symbol portfolio and back to 1/1/2004 (and likely a weak testing methodology). I did not include transaction costs - so as Mike mentions, I believe that this is due to stronger tendency to mean revert with larger absolute distances from the mean, irrespective of the current vol regime - equating to more quality opportunities during high volatility periods. (As in the earlier example, what i'm trying to say is that being down 6% when avg daily vol = 4% is a higher quality signal than being down 3% when avg daily vol = 2%...this is despite both being 1.5x the avg daily range and equally likely to occur within their respective regimes).
I plan on doing a more complete analysis of dynamic position sizing, with the hopes of demonstrating this stronger tendency to mean revert. Admittedly it isn't the most straightforward way of testing this (could do something like compare levels of serial corr in different vol scenarios), but it will be good to get a feel for variable position size. In addition to that potential issue, there is the big one you mention below and the increased transaction costs that Mike also highlighted. Basically it looks like the idea stinks.
Quote from talontrading:
-The behavior of volatility is complex... extremely low volatility conditions can actually lead to explosions in volatility. (this is probably a result of mean reversion.) So... think about this... when volatility is lowest it may be ready to explode... at that time you are putting on your largest position because you size that way.
It does seem to be an improvement, but acknowledging that raises the queston of how does one make money in a prolonged vol crunch?
Also, why is it the ratio to long term vol that matters rather than just the recent realized vol? I would think that the duration of our trades is short enough that vol reverting to its long term mean isn't a consideration. If it is just the recent realized vol that's important, then I guess that would answer the first question - only trade high vol products during a crunch. You're pnl will be reduced because of trading a smaller # of stocks but everything else should remain the same...?
Quote from talontrading:
Question: does this look like a worthwhile addition to the system? Thoughts??
This comment looks like it was intentionally placed, but I'm not sure that I fully understand its consequence. Does this imply that one should be wary of a filter which removes your big losers (you most likely curve fit)? If the big losers were removed after you applied the filter in this instance, would the same logic apply even though the filter was not very selective (number of trades was reduced by 60%)?
Quote from talontrading:
Biggest and smallest trades are no affected.