General the more rules one has , the less likely history will repeat itself.

When running tests on systems...

One method is to run them in batches of 150

Some batches will show a profit & other batches may very well break even.

That way one gets a stronger idea if the plan has any legs or not.

Is also a strong idea to test the price range the winners came from also.
If profit came from say 1-2 outsiders , then the warning bells should be sounding because the system is less likely to repeat that result.

The term Back fitting is often used as a derogatory word to describe a system that was shoe horned into making a profit using a hundred rules over layed on past data .
In other words the data was massaged into profit by adding a hundred rules.
.
I believe seeing that future data is not available then that's all we have to work with.
The question we are then left with, is will these rules repeat themselves into the future.
Some do & some dont,
That's why it is suggested to run the rules over previously unseen data to see if it holds up..

Once we have a lot of races say over 4.5 years , its an idea to batch them into lots on 150 races & see how consistent it may be.
We have all seen systems that absolutely nail it over say a 3 month period , then fall in a hole - Very frustrating.



Here is an example.

Lay Plan
Lay bet all 2nd Favs priced 2.00-4.90 that have a win SR of 20-23% in races with 9+ runners.

What stands out here as possible back fitting, is the 20-23% win SR.

This may tell us the the percentages have been cherry picked ,to force that data into profit.
This may or may not repeat itself.
One would have to then run this against unseen data to see if it holds up.
It may indeed be a loop-hole based on punters over betting these commodities because of this popular percentage range punters & systems ,like to use in their rules.

Because there are only a few rules , there is a strong chance that the data may repeat itself.

That Lay Plan above, is currently showing...
+36% POT
80% SR

__________________
Cheers.