You are absolutely right about speed of adjustment choice. There is a precise way to find the optimal "model re-estimation rate" using maximum-likelihood methods.
Say you have some model for predicting 'something', and you calibrate the model paramters, use statistical tests to make sure they arent overfitted (using regularization methods, cross validation, out-of-sample-testing) whatever.
Those parameters are the 'best' estimate over the period in which you analyzed, so, you apply them to trading during your next period, those parameters will, at best, slowly drift over time.. hopefully they drift slow enough for you to make some money before they are useless.
So, how do you estimate these parameters in the first place? Take a sample of the past N days/months/years? Standard techniques apply equal weight to every point in time, e.g. something that happened 6 months ago will have as much ifluence as parameters on something that happened yesterday. This sucks, to say the least.
You could apply some sort of weighted regression, where the times in the past are weighted by how long ago they happened.. btu the problem here is that something that happened in the middle of the sample, might indeed be more important than something that happened yesterday, but would still have less weighting applied. Better, but still sucks.
Or you could implement stochastic parameter estimation, where you start with some 'initial estimate' and 'initial covariance', normally you set the initial estimates to just 0 and the covariance to some huge number on the diagonals of your parameter cov matrix. Now, every new 'sample' that arives (one day, hour, year, month, nanosecond, etc), you calculate some updated estimate that would fit this sample. and then you reconcile that with the current state estimate. e.g., some of the new observation is an actual model change, and some of it is noise.
Then the choice becomes what you mentioned earlier, track too fast and the model is extremely volatile and useless, track too slow and the model doesnt keep up with the data and becomes useless as well. The tracking speed is determined by the ratio between your observation covariance and your state estimate covariance.
So, using this method you dont estimate moel parameters directly, you only set 'hyper parameters' which affects how the algorithm modifies parameters in real time. These hyper parameters can be optimized via maximum likelihood methds which find the exact point where the tradeoff between bias and variance is minimized.
To sum it up: implementing this actualy reduces the number of parameters i need to optimize, it doesnt add to them.
Also, the stuff I trade does indeed drift during intraday timescales.. so dynamic estimation is critical, also, large overnight changes can affect stuff.. realtime estimation optimally combines all stuff from even point in the past, with everything in the near future (pre-market, opening hour.. etc) so that it tracks better during the day without being biased to whatever the market did during the last week.
Quote from SyndBroker:
How much extra profits will this get you? By doing this you are creating a feedback system and given yourself at least an additional 2 parameters to optimize - the learning rate and the time lag of the new training data you feed it. If the learning rate is too high you could end up with an unstable system as it tries to adapts to quickly to new data. Additionally, your backtesting would now also need to incorporate model optimization - with 2 additional parameters adding 2 additional degrees of freedom and more risk of curve-fitting.
If on the other hand you think that new data would not change ths system too much during any one trading day, they why even bother with this.