Good question. Generally they're correllated. But obviously some things can knock them out of wack, like earnings announcements.
There are some time when the Nasdaq and the Russell will strongly out perform the SandP and the Dow, and that's at the end of a beark market and beginning of a reversal. At such a time you should consistently see the Nasdaq and Russell do better. We're almost seeing that now.
In general I've also heard that at most time the Nasdaq tends to be the leader of the group, but like most things, that changes too I'm sure.
Like for example, at one time the BANK index was leading the market, and at another time it was oil. I think it's important to always know the correlations that do exist. You can throw up a quick comparison chart to see which one's leading the way.