How Has Computer Trading Affected Stock Trading Volume Statistics?

[Stephen Tashi]

Has the advent of computer trading greatly increased the size of statistics for trading volume? - or do those statistics (for individual stocks) somehow omit the flash trades done by computers?

In the pre-computer days, there were people who had theories of stock trading based on both the historical price of a stock and the volume of trades at those prices. I wonder how those people adapted to the computer age.

 

[Bystander]

Twenty years ago the minimum "block" was 100 shares, didn't show on the ticker for anything smaller. Today it's at least one thousand, and there's no transaction size reported. Course that's two different networks, MSNBC, old, and FOX, new.

 

[BWV]

Trading volume has actually declined over the past ten years or so - the increased use of indexed ETFs and mutual funds being the primary reason. The peak of trading volume for the S&P 500 was in 2002. As far as I know, these stats do include off-exchange trading

If by the old theories of stock trading you mean Dow theory and technical analysis - its important to note they were developed in the 20s before laws against insider trading were enacted, the goal of these indicators was to see where the 'smart money' was going.

Before computers, the exchanges often had to close in the late 60s / early 70s to process the trades

 

[Office_Shredder]

Twenty years ago the minimum "block" was 100 shares, didn't show on the ticker for anything smaller. Today it's at least one thousand, and there's no transaction size reported. Course that's two different networks, MSNBC, old, and FOX, new.

Every trade for even one share is reported on the tape with an exact transaction size.