German stock exchange, ETR vs FRA
I still can't understand why there is a price discrepancancy.  There isn't. It's the same stock and price differences between such major exchanges will always be minimal. I think you simply haven't paid attention to the date range. It seems Google finance only has data for FRA:BMW reaching back to 2011, so if you try to look at the development of your investment since 2009, you're not getting comparable data. I stumbled on the same discrepancy, and was puzzled by a significant difference between the two prices on ETR and FRA. For example, today is Sunday, and google shows the following closing prices for DAI. FRA:DAI: ETR:DAI: So it looks like there are indeed two different exchanges trading at different prices.  Now, the important value here, is the last column (Volume). According to Wikipedia, the trading on Frankfort Stock Exchange is done today exclusively via Xetra platform, thus the volume on ETR:DAI is much more important than on FRA:DAI.  Obviously, they Wikipedia is not 100% accurate, i.e. not all trading is done electronically via Xetra. According to their web-page, Frankfort exchange has a Specialist Trading on Frankfurt Floor service which has slightly different trading hours.  I suspect what Google and Yahoo show as Frankfort exchange is this manual trading via a Specialist (opposed to Xetra electronic trading). To answer your question, the stock you're having is exactly the same, meaning if you bought an ETR:BMW you can still sell it on FRA (by calling a FRA Trading Floor Specialist which will probably cost you a fee). On the other hand, for the portfolio valuation and performance assessments you should only use ETR:BMW prices, because it is way more liquid, and thus better reflect the current market valuation.
"Exchange A has 100 shares of a stock at $10, the next 100 shares cost $10.01. Exchange B has the same pricing structure.  A fund manager wants to buy 200 shares of the stock, and decides that buying 100 shares at $10 from each exchange will be cheaper than staying in one exchange and paying $10.01 for the second half of his order.  The manager places two separate orders. Let's say the first order reaches exchange A, and the trade executes at $10. Traders (algorithms) on exchange B see this happen, and adjust their price up to $10.01 accordingly. Now, when the manager's order reaches exchange B, there will no longer be any shares trading at $10.  Some people say that this is front running, but if the manager only wanted 100 shares, the price would have still shifted. Some say this creates a more efficient market with tighter spreads due to the decreased risk to the market maker, but it also means the aggregate bid-ask offers across multiple exchanges are not necessarily accurate, creating a ""false liquidity"". You can decide for yourself whether or not this is a good thing." "Tricky question, basically, you just want to first spread risk around, and then seek abnormal returns after you understand what portions of your portfolio are influenced by (and understand your own investment goals) For a relevant timely example: the German stock exchange and it's equity prices are reaching all time highs, while the Greek asset prices are reaching all time lows. If you just invested in ""Europe"" your portfolio will experience only the mean, while suffering from exchange rate changes. You will likely lose because you arbitrarily invested internationally, for the sake of being international, instead of targeting a key country or sector. Just boils down to more research for you, if you want to be a passive investor you will get passive investor returns. I'm not personally familiar with funds that are good at taking care of this part for you, in the international markets." The suffix represents the stock exchange the stock is traded on. N represents the New York Stock Exchange and O represents the Nasdaq. Sometimes a stock can be listed on more than one exchange so the suffix will give you an indication of which exchange the stock is on. For example the Australian company BHP Billiton Ltd is listed on multiple exchanges so is given a different suffix for the different exchanges (especially when the code is the same for each exchange). Below are a few examples of BHP: I have an example of a trade I made some time ago.  By entering the position as a covered call, I was out of pocket $5.10, and if the stock traded flat, i.e. closed at the same $7.10 16 months hence, I was up 39% or nearly 30%/yr. As compared to the stock holder, if the stock fell 28%, I'd still break even, vs his loss of 28%. Last, if the stock shot up, I'd get 7.50/5.10 or a 47% return, vs the shareholder who would need a price of $10.44 to reflect that return. Of course, a huge jump in the shares, say to $15, would benefit the option buyer, and I would have left money on the table. But this didn't happen. The stock was at $8 at expiration, and I got my 47% return. The option buyer got 50 cents for his $2 bet.  Note, the $2 option price reflected a very high implied volatility. To answer your original question: There is proof out there. Here is a paper from the Federal Reserve Bank of St. Louis that might be worth a read.  It has a lot of references to other publications that might help answer your question(s) about TA.  You can probably read the whole article then research some of the other ones listed there to come up with a conclusion.  Below are some excerpts:  Abstract: This article introduces the subject of technical analysis in the foreign exchange market, with emphasis on its importance for questions of market efficiency.  “Technicians” view their craft, the study of price patterns, as exploiting traders’ psychological regularities.  The literature on technical analysis has established that simple technical trading rules on dollar exchange rates provided 15 years of positive, risk-adjusted returns during the 1970s and 80s before those returns were extinguished.  More recently, more complex and less studied rules have produced    more modest returns for a similar length of time.  Conventional explanations that rely on risk adjustment and/or central bank intervention do not plausibly justify the observed excess returns from following simple technical trading rules.  Psychological biases, however, could contribute to the profitability of these rules. We view the observed pattern of excess returns to technical trading rules as being consistent with an adaptive markets view of the world.    and  The widespread use of technical analysis in foreign exchange (and   other) markets is puzzling because it implies  that either traders are   irrationally making decisions on useless information or that past   prices contain useful  information for trading.  The latter   possibility would contradict the “efficient markets hypothesis,”   which holds that  no trading strategy should be able to generate   unusual profits on publicly available information—such as past    prices—except by bearing unusual risk. And the observed  level of   risk-adjusted profitability measures market  (in)efficiency. Therefore   much research effort has been directed toward determining whether   technical analysis is  indeed profitable or not. One of the earliest   studies, by Fama and Blume (1966), found no evidence that a particular   class of TTRs could earn abnormal profits in the stock market.   However, more recent research by Brock,  Lakonishok and LeBaron (1992)   and Sullivan, Timmermann an d White (1999) has provided contrary   evidence. And  many studies of the foreign exchange market have found   evidence that TTRs can generate persistent profits (Poole  6  (1967),   Dooley and Shafer (1984), Sweeney (1986), Levich and Thomas (1993),   Neely, Weller and Dittmar (1997),  Gençay (1999), Lee, Gleason and   Mathur (2001) and Martin (2001)). First and foremost you need to be aware of what you are comparing. In this case, HSBC as traded on the NYSE exchange is not common shares, but an ADR (American Depository Receipt) with a 5:1 ratio from the actual shares. So for most intents and purposes owning one ADR is like owning five common shares. But for special events like dividends, there may be other considerations, such as the depository bank (the institution that created the ADR) may take a percentage. Further, given that some people, accounts or institutions may be required to invest in a given country or not, there may be some permanent price dislocation between the shares and the ADR, which can further lead to discrepancies which are then highlighted by the seeming difference in dividends. Daily &gt; Weekly &gt; Monthly. This statement says that if you use daily returns you will get more noise than if you used weekly or monthly returns. Much of the research performed uses monthly returns, although weekly returns have been used as well. For HFT you would need to detrend the data in order to spot true turning points. Questrade is a Canada based broker offering US stock exchange transactions as well. It says this right on their homepage. ETFs are traded like stocks, so the answer is yes.  Why did you think they only offered funds?