How Has Computer Trading Affected Stock Trading Volume Statistics?

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Discussion Overview

The discussion centers on the impact of computer trading on stock trading volume statistics, exploring whether these statistics reflect all trading activities, including flash trades, and how historical trading theories have adapted to modern practices. It encompasses theoretical, historical, and statistical perspectives.

Discussion Character

  • Exploratory
  • Debate/contested
  • Historical

Main Points Raised

  • One participant questions whether computer trading has significantly increased trading volume statistics or if certain trades, like flash trades, are omitted from these statistics.
  • Another participant notes that the minimum block size for reporting trades has changed over the years, indicating a shift in how trading data is presented.
  • It is mentioned that trading volume has declined over the past decade, with indexed ETFs and mutual funds being cited as contributing factors, while also asserting that off-exchange trading is included in volume statistics.
  • A reference is made to historical trading theories, such as Dow theory and technical analysis, which were developed before regulations against insider trading, suggesting that these theories aimed to track 'smart money' movements.
  • One participant emphasizes that every trade, regardless of size, is reported on the tape, contradicting earlier claims about transaction size reporting.

Areas of Agreement / Disagreement

Participants express differing views on the effects of computer trading on volume statistics and the historical context of trading theories. There is no consensus on whether trading volume has increased or decreased due to computer trading.

Contextual Notes

There are unresolved assumptions regarding the completeness of trading volume statistics and the definitions of terms like "flash trades" and "block size." The discussion reflects varying interpretations of historical trading practices and their relevance today.

Stephen Tashi
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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.
 
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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.
 
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

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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
 
Bystander said:
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.
 

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