I'm not sure i've ever really seen this discussed on here but I'm sure its something the system aficionado's can provide some answers about.

Basically i've found it easier to create some lay systems have currently have 4 that i'm forward testing and having quite a lot of success with so far. My question becomes that say you have a suite of successful lay systems can you then utilize these to also create backing systems since you obviously do not want to back the lay selections as you have a negative expectancy on them?

Seems fairly logical to me and I don't see an issue with it but just wanted some confirmation from those you have been doing system backing/laying for a longer amount of time successfully.

The reason I ask is i've done some backtesting using really basic rules, for instance backing the top weighted horse that isn't a lay selection and the results are very encouraging.

Yes you can do it. If your using betfair it all comes down to which side you have less selections to handle. If your in a 10 horse race and 6 are lays then bits easier to back 4 selections. If your only going to lay 2 horses then its easier to lay 2 selections.

But it can also come down to %s as well as doing laying 8 horses in a 10 horse race will not make as much as backing the 2 horses. Same the other way around, if you only lay 2 horses then laying will generally give better returns then backing the 8 horses.

If your talking on the TAB then you need to be removing at least 15% (or be getting a rebate to offset the % takeout). In that case just backing will work providing you are removing enough selections to make a profit.

Thanks for the reply UB,

I'm more thinking of backing and laying horses in the same race with something like the following scenario.

12 horse race, out of my 4 lay systems it has 3 horses that I should lay and I have 2 backing systems that select 1 horse to back. This is with the backing systems being built on the basis that you don't back any lay selections - essentially its the first rule.

Probably sounds like a silly question if its fine to take that approach but its just something i'm pondering at the moment. Or would your suggestion simply be rather than backing the horse just stake more on the lays?

Sounds like your mixing up your systems. I would suggest to jsut back/lay them as they suggest otherwise how can you really trust your test data.