What is the difference between FINRA share volume and NASDAQ share volume?
Assuming the data you're referring to is this line: the difference might be related to the different exchanges on which the stock trades.  FINRA could be listing the reported volume from one exchange, while the NASDAQ data might be listing the volume on all exchanges. This is an important distinction because AAV is a Canadian company that is listed on the Toronto Stock Exchange and the NYSE. The Q at the end of the line stands for NASDAQ, according to FINRA's codebook for those data. My guess is that the FINRA data is only reporting the volume for the NASDAQ exchange and not the total volume for all exchanges (Toronto, NASDAQ, NYSE, etc.) while the data straight from NASDAQ, oddly enough, is reporting the total volume. However, FINRA could also face reporting discrepancies, since it's a regulatory body and therefore might not have the most up-to-date volume data that the various exchanges can access.  I don't know if it's related or not, but looking at the NASDAQ historical data, it looks like the volume on March 6, the day you're asking about, was much lower than the volume in most of the days immediately before or after it. For all I know, something might have happened that day concerning that particular stock or the market as a whole. I don't remember anything in particular, but you never know.
"You can do a lot of deduction FINRA keeps a ""REG-SHO"" list created daily that tells what the daily short volume is. March 26th 2014's list: http://regsho.finra.org/FNSQshvol20140326.txt If you are talking about the United States, this answer may be better ;)" I suspect that the times you are referring to are those times when there is relatively low volumes of foreign exchange trading.  Lower volumes of trading make it possible for large orders to have a disproportionate effect on the market price.  This implies that the times to avoid will be the times with the lowest relative volumes.  This will occur on the cusp between the New York market winding down and the Asia/Tokyo market revving up. This will be in the hours preceding Tokyo's opening at 06:00 Tokyo time, so the time to avoid is about 04:00-06:00 Tokyo time, or about 20:00-22:00 GMT (if I've worked out the time difference correctly). Foreign exchange is a 24 hour, global market.  Although each of the three main trading centres - London, New York, Asia - will operate 24 hours a day, they will maintain only a skeleton staff outside of normal working hours.  The time difference between London and New York is only 5 hours, so there is no period of time when both centres are operating with a skeleton staff.  The time difference between London and Tokyo is 8 hours, so again there is no period of time when both centres are operating with a skeleton staff.  The time difference between New York and Tokyo is 13 hours.  This does include a period where both centres are operating with a skeleton staff, as well as London operating on a skeleton staff.  Thus, in the couple of hours immediately preceding Tokyo's opening for the regular trading day there is minimal coverage in each of the three main trading centres.  As mentioned above, this is the time when large orders can have a disproportionate effect on fx rates and so this is the time to avoid. "You can infer some of the answers to your questions from the BATS exchange's market data page and its associated help page.  (I'm pretty sure a page like this exists on each stock exchange's website; BATS just happens to be the one I'm used to looking at.) The Matched Volume section refers to all trades on a given date that took place on ""lit"" exchanges; that is, where a public protected US stock exchange's matching engine helped a buyer and a seller find each other.  Because there are exactly 11 such exchanges in existence, it's easy to show 100% of the matched volume broken down into 11 rows. The FINRA & TRF Volume section refers to all trades on a given date that took place on ""non-lit"" exchanges.  These types of trades include dark pool volume and any other trade that is not required to take place in public but is required to be reported (the R in TRF) to FINRA.  There are three venues via which these trades may be reported to FINRA -- NASDAQ's, NYSE's, and FINRA's own ADF.  They're all operated under the purview of FINRA, so the fact that they're ""located at"" NASDAQ or NYSE is a red herring.  (For example, from the volume data it's clear that the NASDAQ facility does not only handle NASDAQ-listed (Tape C) securities, nor does the NYSE facility only handle NYSE-listed (Tape A) securities or anything like that.) The number of institutions reporting to each of the TRFs is large -- many more than the 11 public exchanges -- so the TRF data is not broken down further.  (Also I think the whole point of the TRFs is to report in secret.)  I don't know enough details to say why the NASDTRF has always handled more reporting volume than the other two facilities.  Of course, since we can't see inside the TRF reporting anyway, it's sort of a moot point." NSCC illiquid charges are charges that apply to the trading of low-priced over-the counter (OTC) securities with low volumes. Open net buy quantity represents the total unsettled share amount per stock at any given time during a 3-day settlement cycle. Open net buy quantity must be less than 5,000,000 shares per stock for your entire firm Basically, you can't hold a long position of more than 5 million shares in an illiquid OTC stock without facing a fee. You'll still be assessed this fee if you accumulate a long position of this size by breaking your purchase up into multiple transactions. Open net sell quantity represents the total unsettled share amount per stock at any given time during a 3-day settlement cycle. Open net sell quantity must be less than 10% percent of the 20-day average volume If you attempt to sell a number of shares greater than 10% of the stock's average volume over the last 20 days, you'll also be assessed a fee. The first link I included above is just an example, but it makes the important point: you may still be assessed a fee for trading OTC stocks even if your account doesn't meet the criteria because these restrictions are applied at the level of the clearing firm, not the individual client.  This means that if other investors with your broker, or even at another broker that happens to use the same clearing firm, purchase more than 5 million shares in an individual OTC stock at the same time, all of your accounts may face fees, even though individually, you don't exceed the limits. Technically, these fees are assessed to the clearing firm, not the individual investor, but usually the clearing firm will pass the fees along to the broker (and possibly add other charges as well), and the broker will charge a fee to the individual account(s) that triggered the restriction. Also, remember that when buying OTC/pink sheet stocks, your ability to buy or sell is also contingent on finding someone else to buy from/sell to. If you purchase 10,000 shares one day and attempt to sell them sometime in the future, but there aren't enough buyers to buy all 10,000 from you, you might not be able to complete your order at the desired price, or even at all. Large volume just means a lot of market participants believe they know where the stock price will be (after some amount of time).  The fact that the price is not moving just means that about 50% of those really confident traders think the stock will be moving up, and about 50% of those really confident traders think the stock will be moving down. At the bottom of the page you linked to, NASDAQ provides a link to this page on nasdaqtrader.com, which states Each FINRA member firm is required to report its “total” short interest positions in all customer and proprietary accounts in NASDAQ-listed securities twice a month. These reports are used to calculate short interest in NASDAQ stocks. FINRA member firms are required to report their short positions as of settlement on (1) the 15th of each month, or the preceding business day if the 15th is not a business day, and (2) as of settlement on the last business day of the month.* The reports must be filed by the second business day after the reporting settlement date. FINRA compiles the short interest data and provides it for publication on the 8th business day after the reporting settlement date. The dates you are seeing are the dates the member firms settled their trades. In general (also from nasdaq.com), the settlement date is The date on which payment is made to settle a trade. For stocks traded on US exchanges, settlement is currently three business days after the trade. Well the thing to understand about HFT is that the volume levels heavily affect not just the earnings but also the ecosystem. HFT is almost always liquidity constrained so the volume and volatility is going to affect the overall profitability of the strategy since less of these things means fewer and smaller trading opportunities.  Since 2008 volume and volatility have been heavily negatively correlated with risk-on/risk-off. During risk-off periods investors seem to panic and trading hits a frentic pace. This describes late 2008 and more recently August 2011. Even in 2012 the highest volume/volatility period was in May when the Euro deals were in danger. Risk-on environments tend to be marked be calm, orderly buying.  Second the dark pool issue is bringing liquidity out of the lit markets where HFT normally makes its money. The primary reason for this trend is that dark pools are allowed to offer sub-penny quotes whereas lit exchanges are not. Because of this arbitrary regulatory constraint most of the time dark pools are going to offer better prices, especially on thick book securities.  But beyond that the level of volume effects some HFT players more heavily then others. Imagine all the HFT firms as a pride of lions. When volume is high and liquidity is flowing it's like the pride has brought in a giant water buffalo. The biggest, baddest cats eat first, but there's still food left for the cubs after they're finished feeding.  But if the pride only brings in say a baby gazelle the alpha cats will eat everything and the runts will go hungry. That basically describes what's happening now. A firm like RennTech or GETCO will make less money in a low volume environment, but still do fine. Marginal firms like Eladian will lose the ability to make any money.  Since the marginal firms need the press and the dominant firms tend to be more secretive than the NSA, you'll tend to read more about the former than the latter. "Regarding SPY: ""One SPDR unit is valued at approximately 1/10 of the value of the S&P 500. Dividends are distributed quarterly, and are based on the accumulated stock dividends held in trust, less any expenses of the trust.""  (source)  These are depository receipts, not the actual stocks. Regarding IVV: ""The component stocks are weighted according to the total float-adjusted market value of their outstanding shares. The Fund invests in sectors, such as energy, information technology, industrials, financials, consumer staples, healthcare, telecom services, consumer discretionary and materials.""  (more here) VOO is the Vanguard S&P 500 ETF. The tracking error seems pretty small to me.  I went to Google Finance and plotted the percent change for all four on one chart.  They lie pretty much on top of one another.  The actual dollar value of each one doesn't matter nearly as much as the fact that they move up and down almost in lock-step.  There may be a larger difference going farther out, but for three separate financial products, the agreement is still remarkably good."