Quote from kcll:
That's just my perception without strict justification. What do you think about it?
Programs don't make trading more sophisticated; they just carry out the intentions of a human in an algorithmic fashion. Woo-hoo!
As a scalper, I am very aware of the effect programs have on stocks: even though 80% of the NYSE's volume is program trading, it's still purely a game of reading people's intentions. Sometimes a program will join you with whatever bid you put in. Sometimes the program will bid higher than you. So if you're long a stock, you put in a small bid for 100 shares and the program joins you. Then, you bid higher, and the program chases you. You keep doing this until the program stops joining you, and then you pull your bid while simultaneously selling to the computer you just tricked into paying a higher than necessasary price. It's not always that simple - sometimes you put the bid in, get filled, and then the program stops... but that kind of activity doesn't make the market "more sophisticated."
Most the programs are add-liquidity boxes which put in bids/offers... other programs will bring bids in at higher levels, or offers at lower levels, and switch which market place (ECNs, NYSE, etc.) the order is on.
An interesting buy program I've seen is one that buys stock when I buy. If I buy 200 shares at 32.12, the program buys 200 shares immediately; if I buy 400, the program buys 400. It always buys at the same price I buy at, never high, and always the same size or less (less if there is no more available at a given price level). What does that tell me? That some guy is trying to accumulate stock. Will the stock go up? Maybe, but probably not because of the buy program - it's just one bullish indicator - but it doesn't tell me the strength of the sellers.
Until computers have AI that is actually SMARTER than humans, which is a long way off, trading will be dominated by humans.
Anyone who purports that (I don't meant this to sound like a snob or an elitest at all) program trading makes traidng "more complicated" is probably not that familiar with the dynamics of a marketplace.