US market volume has been expanding since enormously since 2005. There has been a lot of scuttlebutt this year regarding a lack of volume, usually referring to NYSE trading because of its availability. The chart below shows NYSE floor volume as reported by the exchange in red (this is the same number you would find on WSJ.com or any other data provider). As shown, NYSE volume is largely unchanged since 2000 because there are actually four key stock exchanges in the US: the New York Stock Exchange, the NASDAQ, the NYSE Arca, and the FINRA ADF. Birinyi Associates has been a long-time commentator on structural changes occurring in the market; the pinnacle of that work being "the Next Crash."
By digging deeper and looking at total volume for NYSE issues we find that there is significantly more trading than many people realize. To calculate total volume, shown below in green, we added shares traded on all US exchanges for each NYSE listed stock, and then added all of the stocks' volumes for a given day. Using this methodology we find that on 11/6/09 total volume for NYSE issues was actually 4.89 billion shares versus NYSE volume of 1.29 billion shares.
We realize that this shift in volume is becoming more widely publicized, and that this post is not groundbreaking, but we also note that any analysis using volume to confirm a market's move should be scrutinized.