Quote from logic_man:
I think it's a terminology thing and that the word "function" wasn't appropriate there because it has another meaning which doesn't align with what I was asking. What I meant is whether or not that poster thought that the cessation of the strategy's ability to capture profits was a reflection of the underlying fact that the parameters in the model only temporarily happened to enable profitable trades due to some temporary luck and that the parameters weren't measuring anything "fundamental" at all.
What I meant by "signal" is the useful information in the data as opposed to the noise. What I meant by long term signal is this: a finite support signal can only contain wavelengths up to the window length and will lack frequencies lower than that. So a low pass filter on a windowed signal really is a band pass with the lower frequency cutoff dictated by the window length. A sudden loss in profitability could be construed as a change in the characteristics of the price distributions (non-stationarity) OR it could be that there were longer term signals that were missed in the original time series due to the finite training window length.
