I would think it depends on what scale you're looking at. It is pretty obvious that if one guy takes out a large chunk of the order book of one security, over the course of seconds, on only one side of the market, the price is going to move. If we're talking about the S&P 500 dropping over the course of a few months, I think it is accurate to say that those who want to sell are outnumbering those who want to buy.