Not so useless: you can construct hadge fund-like trading strategies with the DOW and SP500. Both DOW and SP500 have some tendency to go up and down at the sam

Not so useless: you can construct hadge fund-like trading strategies with the DOW and SP500. Both DOW and SP500 have some tendency to go up and down at the same time in bull and bear market times. When this happens you can (for instance) short DOW and long SP500 and your losses in the sort side will be covered by the gains in the logn side... ...but they will be uncorrelated for short periods of time. So, if your short possition goes down while your long is constant or goes down much slower than your short, then you're making money. Probably you can make this kind of hedging with very little money (or almost free) using the fee you get from going short to buy the long leg of the spread.