Quote from FaceOff:
Anything which stops you entering trades is actually reducing your sample-size in back-testing, which will lead to curve-fitting. So to test if filters are working, use walk-forward testing.
Quote from jprad:
Agree, to a point.
Switching a fairly simple trading system on or off based on it's equity curve can lead to a more robust result than adding additional filters directly to the system's trading rules.
Like anything else though, YMMV...
Quote from Dobbes:
What is the general opinion on using filters in simple technical systems? Do they add value in general, or are they just another source of curve-fitting?