Quote from rufus_4000:
Okay, I will jump in I guess.
The strict definition of NYSE program trading (something called a program trading report) is any trade that consists of over 15 different stocks, or over $1M in value. That's it. However, around sometime in 2003, NYSE sent out a circular indicating that any "pair-based" trades need to be reported as Program Trades, this sent shivers down the NYSE members. Problem is that nobody wants to be fined for non-compliance, so firms started to over report (the ibank I was at debated to report *every* trade with more than 2 stocks, regardless of amount, as Program Trades), effectively causing program trading percentage to increase dramatically. So much so, that in fact NYSE indicated in 08/2004 that it would start audit the program trading reports as a part of the annual audit, and would fine members if they determined that the members are over reporting. I used to have all the circulars, look them up on NYSE if you care.
So this would explain partially why program trading % are increasing rapidly. It is true that Program Trading is increasing, just not that rapidly, it is an approximate indication that both principal and customers are trading the complex (baskets, pairs, arbs, etc), rather than individual stocks. Stat arb probably consist a lot of the "other arb" strategies, from what I know of the prop desks at ibanks and quant based hedge funds.
However, as NYSE goes full-speed to a full-hybrid model (Jan '06 being the starting date), most of the Specialist business will be run from the upstairs algorithms starting on 2006, and the "$2 brokers" are wondering where their jobs will go after the crowd thins out. The NYSE members see what happened to CME and CBOT pits after Globex and eCBOT (failed ACE, blah, blah), so they know what is coming in 1-2 years.