I totally agree with Jonnyt.
There is a significant difference between backtesting using the cash index and futures. The cash index really does flatter any system. Basically the futures move around a lot more than the cash and the futures data will also take account of the bid/ask spread. Obviously for spreadbetting you need to add a few more points in each direction to account for the increased spread that they offer.
Basically there will be times when you narrowly escape being stopped out on the cash index but which would be stopped on the futures. These will make a big difference to your overall results.
If you do want to use the cash to simulate SB prices then I suggest you allow 10 pts each way for testing. So if your long and your stop is 10400, count it as stopped out at 10400 if the cash price hits 10410. If your still profitable then, then your probably on to a winner!
There is a significant difference between backtesting using the cash index and futures. The cash index really does flatter any system. Basically the futures move around a lot more than the cash and the futures data will also take account of the bid/ask spread. Obviously for spreadbetting you need to add a few more points in each direction to account for the increased spread that they offer.
Basically there will be times when you narrowly escape being stopped out on the cash index but which would be stopped on the futures. These will make a big difference to your overall results.
If you do want to use the cash to simulate SB prices then I suggest you allow 10 pts each way for testing. So if your long and your stop is 10400, count it as stopped out at 10400 if the cash price hits 10410. If your still profitable then, then your probably on to a winner!