What makes a stock get 40 times avg daily volume without any news?
"Probably the biggest driver of the increased volumes that day was a change in sentiment towards the healthcare sector as a whole that caused many healthcare companies to experience higher volumes ( https://www.bloomberg.com/press-releases/2017-07-11/asset-acquisitions-accelerate-in-healthcare-sector-boosting-potential-revenue-growth ). Following any spike, not just sentiment related spikes, the market tends to bounce back to about where it had been previously as analysts at the investment banks start to see the stock(s) as being overbought or oversold. This is because the effect of a spike on underlying ratios such as the Sharpe ratio or the PE ratio makes the stock look less attractive to buyers and more attractive to sellers, including short sellers. Note, however, that the price is broadly still a little higher than it was before the spike as a result of this change in sentiment. Looking at the price trends on Bloomberg (https://www.bloomberg.com/quote/CDNA:US) the price had been steadily falling for the year prior to the spike but was levelling out at just over $1 in the few months immediately prior to the spike. The increased interest in the sector and the stock likely added to a general change in the direction of the price trend and caused traders (as opposed to investors) to believe that there was a change in the price trend. This will have lead to them trading the stock more heavily intraday exacerbating the spike. Note that there traders will include HFT bots as well as human traders. You question the legality of this volume increase but the simple answer is that we may never know if it was the target of traders manipulating the price or a case of insider trading. What we can see is that (taking ""animal spirits"" into account) without any evidence of illegality there are plenty of potential reasons why the spike may have occurred. Spikes are common where traders perceive a change in a trend as they rush to cash in on the change before other traders can and then sell out quickly when they realise that the price is fundamentally out of sync with the firm's underlying position. You yourself say that you have been watching the stock for some time and, by that fact alone, it is likely that others are for the same reasons that you are. Otherwise you wouldn't be looking at it. Where people are looking at a stock expecting it to take off or drop you expect volatility and volatility means spikes!"
"No, a jump in market capitalization does not equal the amount that has been invested.  Market cap is simply the stock price times the total number of shares. This represents a theoretical value of the company. I say ""theoretical"" because the company might not be able to be sold for that at all.  The quoted stock price is simply what the last buyer and seller of stock agreed upon for the price of their trade. They really only represent themselves; other investors may decide that the stock is worth more or less than that.  The stock price can move on very little volume. In this case, Amazon had released a very good earnings report after the bell yesterday, and the price jumped in after hours trading. The stock price is up, but that simply means that the few shares traded overnight sold for much higher than the closing price yesterday.  After the market opens today and many more shares are traded, we'll get a better idea what large numbers of investors feel about the price. But no matter what the price does, the change in market cap does not equal the amount of new money being invested in the company. Market cap is the price of the most recent trades extrapolated out across all the shares." I used to be a trader at a desk that sold delta-one derivatives on listed indices (think swaps, ETFs). There is a LOT to do:   buy/ sell stocks according to redemptions or new orders; manage the currency exposure; indices rebalance their composition everyday based on stock corporate actions, dividends and index reviews - you need to be aware of each and everyone and rebalance your portfolio to account for it; manage your inventory to get the best repo rates possible; trade single stock swaps with foreign counterparties to get access to better tax rates on dividends; when you have a big order where certain stock orders may not get filled - you have to create a strategy for managing that risk; sometimes you hedge your positions using futures that expire every three months in which case you need to figure out the best times to roll your expiring futures; i could go on and on.  Basically, since the profit margins are so low, the market so competitive for such vanilla products, and the volumes so high, you have to really make your processes super efficient and error-proof. Trust me, there is a lot to be done! There are multiple factors at play that drive stock price movements, but one that can be visualized is that stocks can be priced relative to other (similar stocks).  When one stock price goes up without fundamental changes (i.e. daily market noise/movements), it becomes slightly more expensive relative to it's peers.  Opportunists will sell the now slightly more expensive stock, while others may buying the slightly cheaper (relatively) peer stock.    Imagine millions of transactions like this happening throughout each hour, downward selling pressure on a stock that rises too fast in value relative to it's peers or the market, and upward buying pressure on stocks that are relatively cheaper than it's peers.  It pushes two stocks towards an equilibrium that is directionally the same.    Another way to think of it is lets say tomorrow there is $10B in net new dollars moved into buy orders for stocks that comes from net selling of bonds (this is also partly why bonds/stocks are generally inversely related).  That money goes to buys stocks ABC, XYZ, EFG.  As the price of those goes up with more buying pressure, stocks JKL, MNO, PQR are relatively a tad cheaper, so some money starts to flow into there.  Repeat until you get a large majority of the stocks that buyers are willing to buy and you can see why stocks move in the same direction a lot of times. Well, it was a 3 wheeler and looked too funky for current tastes and without mandates or complete revolution in infrastructure and so forth it's sad to say it won't work here. And again, you can buy many cars that get 40+ MPG without being hybrid....when I look at the Volt I ask, why, if the avg. MPG is 42....build something more like an Accord or Civic that gets 40+ mpg...  I'm looking ahead when battery technology will make the breakthroughs for mass scale, much more durable, longer charge and life times such as this, in maybe 2017;  http://www.bbc.co.uk/news/technology-15735478  We just need to be patient, make heavy investment in R&amp;D...and focus it on the areas that will make and break us. "With my current, limited knowledge (see end), I understand it the following way: Are share prices really described as ""memoryless""?  Yes.  Is there a   technical meaning of the term? What does it really mean? The meaning comes from Markov Models: Think of the behavior of the stock market over time as a Markov Chain, i.e. a probabilistic model with states and probabilistic transitions. A state is the current price of all stocks of the market, a transition is a step in time. Memoryless means that transitions that the stock market might make can be modelled by a relation from one state to another, i.e. it only depends on the current state. The model is a Markov Chain, as opposed to a more general Stochastic Process where the next state depends on more than the current state. So in a Markov Chain, all the history of one stock is ""encoded"" already in its current price (more precisely in all stock's prices).  The memorylessness of stocks is the main statement of the Efficient Market Theory (EMT). If a company's circumstances don't change, then a drop in its share price is going to be followed by a rise later.  So if the EMT holds, your statement above is not necessarily true. I personally belief the EMT is a good approximation - only large corporations (e.g. Renaissance Technologies) have enough ressources (hundreds of mathematicians, billions of $) to be able to leverage tiny non-random movements that stem from a not completely random, mostly chaotic market.  The prices can of course change when the company's circumstances change, but they aren't ""memoryless"" either. A company's future state is influenced by its past. In the EMT, a stock's future state is only influenced by its past as much as is encoded in its current price (more precisely, the complete market's current state). Whether that price was reached by a drop or a rise makes no difference.  The above is my believe, but I'm by far no finance expert. I am working professionally with probabilistic models, but have only read one book on finance: Kommer's ""Souverän investieren mit Indexfonds und ETFs"". It's supposed to contain many statements of Malkiel's ""A Random Walk Down Wall Street""." I hovered over the label for trading volume and the following message popped up: Volume / average volume  Volume is the number of shares traded on the   latest trading day. The average volume is measured over 30 days. "There's the question whether knowledge about unannounced products is actually ""material"" if everyone (the public) knows that something new will be released. If you work at Apple on the development of the iPhone 8, that's not material. If you worked at Apple and you knew that they stopped developing new phones, that would be very, very, very material information.  The important thing as far as the stock market is concerned is what sales look like, and that's not something you know as a product developer." "Note: the answer below is speculative and not based on any first-hand knowledge of pump-and-dump schemes. The explanation with spamming doesn't really makes sense for me. Often you see a stock jump 30% or more in a single day at a particular moment in time. Unlikely that random people read their emails at that time and decide to buy. What I think happens is the pumper does a somewhat risky thing: starts buying a lot of shares of a stock that has declined a lot and had low volumes during the previous days. As the price starts to increase other people start to notice the jump and join the buying spree (also don't forget that some probably use buy-stop orders which are triggered when the price reaches a particular level). Also there should be some automatic trading involved (maybe HFT firms do pump-and-dumps) as you have to trade a big volume in a relatively short time span. I think it is unlikely to be done by human operators. Another explanation would be that there is a group of pumpers (to spread the risk so to speak). Update: As I think more of it, it is not necessary to buy ""a lot of shares"". You could buy some shares, sell them to another pumper and buy from them again at a higher price in several iterations. I think this could also work if you do it fast enough. These scheme makes sense only you previously bought many shares at the low price, possibly during several weeks. Once the price is pumped high enough you can start selling the shares you previously bought (in the days preceding the pump)."