Hi stebbo & crash.

I agree stebbo in sticking to the rules and carrying on through the bad patches, provided you have a solid history of profits.
This has happened to me on many occasions and I think it's more appropriate to the longer priced horses especially, where one can have a very long run of outs.

crash,

I see where you're coming from regarding backfitting.
There is a solution to this for the database user.
Split the database up into a half or quarter of RANDOM results.
Test your theories, then apply it to the entire database and see if it holds up.
Also I tend to test my filters on various systems to make sure they hold up in general.