We track the S&P in the same way you tried to: if we think it's going to go up, we go up. It's hard to find a correlation using end-of-day info for both because we end at different times, so unless someone shows you minute-to-minute back-tests they're not giving you the full picture.
But watch the Wall Street Daily:
http://www.igindex.co.uk/ And check it against our ALSI on Easy Trader. Most days, you'll see us track it within minutes if not seconds, *even when the US markets are asleep* because it's the closest thing we have to knowing where they'll go when they open. We usually differ if there's a strong-enough non-US driver, but in the absence of locally related news, we're pretty darned correlated. And watch what happens when the US opens. They jump up, we'll very often follow. If we were down, we'll move higher even if we don't go positive.
Either we're getting the inside news at the same time as them, or we're following or anticipating them. Result is the same. Yes, there will be exceptions, but personally I don't like trading unless I can see what the overseas reactions are.
