I backtest with a feasible amount, like 50% of the total the TF of the chart allows. Could be 3 months for 1 minute charts.
When I am satisfied and dead-sure I did not over-optimise, I run the full length, in this example 6 months. Usually with that I prove myself wrong and I over-optimised after all.
Then I go back to the 50% and apply the theory of what I saw wrong in the full length BackTest. Done ? then retry the full length.
For me this leads to robust systems.
or maybe did you try to get a robust system which could be flexible (that could work no matter the market state provided some variables were adapted to this state) but for which you would need to reoptomize the variables once in a while when the system seem to outperform or to make it fit some market state changes?
Never. IMO you won’t be able to tell when the market changed in a fashion that your system won’t recover. It is just not the way to go.
It must be able to cope with all conditions, which hopefully appear sufficiently in your backtesting period (the 100%).
In the very end I don’t recognize changed markets. Yea, for my manual trading ! and if you apply too much of that in your algorithms, then you will go under.
It really is not easy …
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