Thank you for this. Different, probably dumb, question. Again a yes or no would be fine as no doubt your academic duties are keeping you busy. I am currently filtering instruments with the help of the various tiebreakers in your book plus some shortcuts. For example, even before optimising forecast weights, I notice that the returns from some instruments are massively negative in a particular rule class for TF strategies (ranging from -15->-30% over all history). Could I be criticised for backfitting by excluding these at the outset and not letting the optimiser downweight (presumably to zero)?