Errant Routing
On September 30th, Google's share price dropped 10 percent in the space of five minutes before Nasdaq intervened and, attributing the drop in price to an error, cancelled all transactions for that time period. This has left some day traders suspicious - and understandably upset if the cancelled trades would have made them money. (Check out the angry comments at the bottom of this article).
While it remains unclear what caused the initial erroneous price - a fat-finger entry is always possible - Mark Palmer, CEO of StreamBase says that smart order routing accounts for the sudden and dramatic drop of 10 percent. Routers are programmed to notice any changes in price and will act immediately - often in milliseconds to a perceived shift in the market. Thus a fat-finger mistake while entering an order - whether it is too high a volume or too low a price can trigger a momentum in the markets. The herd mentality of trading algorithms is no different to that in the pit - when one player appears to be dumping stock, everyone else jumps on the bandwagon. The difference is that in the algorithmic trading world, it all happens a lot faster.
A similar example of errant routing occurred earlier in September when an outdated story about United Airlines’ 2002 bankruptcy filing was mistaken for breaking news and drove the airline’s stock price down from $12.30 to $3. A human error led to this story being entered into a subscription letter that was distributed by Bloomberg and thus feeds into countless firms’ algorithmic trading engines. These engines are programmed to react instantly to market-changing news such as bankruptcies and went into a selling frenzy to get out of their UA positions.
At the end of the day, these trading engines and routers were doing exactly what they were programmed to do. It doesn’t make sense to blame the computers, they are programmed by people after all. What matters is making sure that they are acting on accurate and timely information. As for fat-finger mistakes, there is really little that can be done about those.