It tin dismiss appear a flake ironic that nosotros should live on discussing Nassim Taleb's best-seller "
Antifragile" here, since around algorithmic trading strategies involve predictions as well as won't live on met alongside blessing from Taleb. Predictions, equally Taleb would say, are "fragile" -- they are prone to diverse biases (e.g. information snooping bias) as well as the occasional Black Swan consequence volition wipe out the small-scale cumulative profits from many right bets. Nevertheless, underneath the heap of diatribes against diverse luminaries ranging from Robert Merton to Paul Krugman, nosotros tin dismiss observe a few gems. Let me start from the obvious to the subtle:
1) Momentum strategies are to a greater extent than antifragile than mean-reversion strategies.
Taleb didn't tell that, but that's the starting fourth dimension idea that came to my mind. As I argued inwards many places, hateful reverting strategies receive got natural lucre caps (exit when toll has reverted to mean) but no natural halt losses (we should purchase to a greater extent than of something if it gets cheaper), then it is real much plain of report to
left tail risk, but cannot accept payoff of the unexpected skilful fortune of the
right tail. Very frail indeed! On the contrary, momentum strategies receive got natural halt losses (exit when momentum reverses) as well as no natural lucre caps (keep same seat equally long equally momentum persists). Generally, real antifragile! Except: what if during a trading halt (due to the daily overnight gap, or circuit breakers), nosotros can't move out a momentum seat inwards time? Well, you lot tin dismiss ever purchase an pick to copy a halt loss. Taleb would sure enough approve of that.
2) High frequency strategies are to a greater extent than antifragile than depression frequency strategies.
Taleb equally good didn't tell that, as well as it has zippo to produce alongside whether it is easier to predict short-term vs. long-term returns. Since HF strategies let us to accumulate profits much faster than depression frequency ones, nosotros withdraw non apply whatever leverage. So fifty-fifty when nosotros are unlucky plenty to live on asset a seat of the incorrect sign when a Black Swan hits, the harm volition live on small-scale compared to the cumulative profits. So spell HF strategies produce non precisely produce goodness from right tail risk, they are at to the lowest degree robust alongside observe to left tail risk.
3) Parameter estimation errors as well as vulnerability to them should live on explicitly incorporated inwards a backtest functioning measurement.
Suppose your trading model has a few parameters which you lot estimated/optimized using about historical information set. Based on these optimized parameters, you lot compute the Sharpe ratio of your model on this same data. No uncertainty this Sharpe ratio volition live on real good, due to the in-sample optimization. If you lot apply this model alongside those optimized the parameters on out-of-sample data, you lot would in all probability acquire a worse Sharpe ratio which is to a greater extent than predictive. But why halt at but ii information sets? We tin dismiss observe northward unlike information sets of the same size, calculate the optimized parameters on each of them, but compute the Sharpe ratios over the N-1 out-of-sample information sets. Finally, you lot tin dismiss average over all these Sharpe ratios. If your trading model is fragile, you lot volition observe that this Sharpe ratio is quite low. But to a greater extent than of import than Sharpe ratios, you lot should compute the maximum drawdown based on each laid of parameters, as well as equally good the maximum of all these max drawdowns. If your trading model is fragile, this maximum of maximum drawdowns is probable to live on quite scary.
The scheme I described higher upwards is called cross-validation as well as is well-known earlier Taleb, though his mass reminds me of its importance.
4) Notwithstanding 3) above, a truthful approximate of the max drawdown is impossible because it depends on the approximate of the probability of rare events. As Taleb mentioned, fifty-fifty inwards illustration of a normal distribution, if the "true" touchstone departure is higher than your approximate past times a mere 5%, the probability of a 6-sigma consequence volition live on increased past times five times over your estimate! So actually the solely means to ensure that our maximum drawdown volition non orbit a sure limit is through
Constant Proportion Portfolio Insurance: trading risky assets alongside Kelly-leverage inwards a express liability company, putting coin that you lot never desire to lose inwards a FDIC-insured bank, alongside regular withdrawals from the LLC to the depository fiscal establishment (but non the other means around).
5) Correlations are impossible to estimate/predict. The solely affair nosotros tin dismiss produce is to brusk at +1 as well as purchase at -1.
Taleb hates Markowitz portfolio optimization, as well as 1 of the reasons is that it relies on estimates of covariances of asset returns. As he said, a dyad of assets that may receive got -0.2 correlation over a long catamenia tin dismiss receive got +0.8 correlation over about other long period. This is particularly truthful inwards times of fiscal stress. I quite handgrip on this point: I believe that manually assigning correlations alongside values of +/-0.75, +/-0.5, +/-0.25, 0 to entries of the correlation matrix based on "intuition" (fundamental knowledge) tin dismiss generate equally skilful
out-of-sample functioning equally whatever meticulously estimated numbers.The to a greater extent than fascinating query is whether in that location is indeed mean-reversion of correlations. And if so, what instruments tin dismiss nosotros move to lucre from it? Perhaps this
article volition help.
6) Backtest tin dismiss solely live on used to spend upwards a strategy, non to predict its success.
This echoes the indicate made past times commenter Michael Harris inwards a previous
article. Since historical information volition never live on long plenty to capture all the possible Black Swan events that tin dismiss occur inwards the future, nosotros tin dismiss never know if a strategy volition neglect miserably. However, if a strategy already failed inwards a backtest, nosotros tin dismiss live on pretty sure that it volition neglect 1 time to a greater extent than inwards the future.
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The online "Quantitative Momentum Strategies” workshop that I mentioned inwards the previous
article is straightaway fully booked. Based on pop demand, I volition offering a "Mean Reversion Strategies" workshop inwards May. Once again, it volition live on conducted inwards real-time through Skype, as well as the pose out of attendees volition live on similarly express to 4. See
here for to a greater extent than information.