Yahoo Finance - Data inconsistencies between historic and current data
You might have better luck using Quandl as a source.  They have free databases, you just need to register to access them.  They also have good api's, easier to use than the yahoo api's Their WIKI database of stock prices is curated and things like this are fixed (www.quandl.com/WIKI ), but I'm not sure that covers the London stock exchange.  They do, however, have other databases that cover the London stock exchange.
"Thanks for pointing out [the study](http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1748851). It's a slightly different cause than what I was describing when I posted this. Specifically, they show an effect not when the names get confused, but rather when the name similarity simply brings more attention to the stock. I was surprised nobody mentioned that in response to my post.  But also interesting is that they had to control for simple confusion between stock symbols, which implies that ticker confusion has a known effect. So I dug into research on that and quickly found [this study](http://www.efmaefm.org/0EFMAMEETINGS/EFMA%20ANNUAL%20MEETINGS/2010-Aarhus/EFMA2010_0161_fullpaper.pdf) found ""a high positive correlation between returns on two matching stocks with similar ticker symbols""." You can get this data from a variety of sources, but likely not all from 1 source.  Yahoo is a good source, as is Google, but some stock markets also give away some of this data, and there's foreign websites which provide data for foreign exchanges.    Some Googling is required, as is knowledge of web scraping (R, Python, Ruby or Perl are great tools for this...). "Remember that in most news outlets journalists do not get to pick the titles of their articles.  That's up to the editor.  So even though the article was primarily about ETFs, the reporter made the mistake of including some tangential references to mutual funds.  The editor then saw that the article talked about ETFs and mutual funds and -- knowing even less about the subject matter than the reporter, but recognizing that more readers' eyeballs would be attracted to a headline about mutual funds than to a headline about ETFs -- went with the ""shocking"" headline about the former. In any case, as you already pointed out, ETFs need to know their value throughout the day, as do the investors in that ETF.  Even momentary outages of price sources can be disastrous. Although mutual funds do not generally make transactions throughout the day, and fund investors are not typically interested in the fund's NAV more than once per day, the fund managers don't just sit around all day doing nothing and then press a couple buttons before the market closes.  They do watch their NAV very closely during the day and think very carefully about which buttons to press at the end of the day.  If their source of stock price data goes offline, then they're impacted almost as severely as -- if less visibly than -- an ETF. Asking Yahoo for prices seems straightforward, but (1) you get what you pay for, and (2) these fund companies are built on massive automated infrastructures that expect to receive their data from a certain source in a certain way at a certain time.  (And they pay a lot of money in order to be able to expect that.)  It would be quite difficult to just feed in manual data, although in the end I suspect some of these companies did just that.  Either they fell back to a secondary data supplier, or they manually constructed datasets for their programs to consume." http://www.euroinvestor.com/exchanges/nasdaq/macromedia-inc/41408/history will work as DumbCoder states, but didn't contain LEHMQ (Lehman Brother's holding company). You can use Yahoo for companies that have declared bankruptcy, such as Lehman Brothers: http://finance.yahoo.com/q/hp?s=LEHMQ&a=08&b=01&c=2008&d=08&e=30&f=2008&g=d but you have to know the symbol of the holding company. The last column in the source data is volume (the number of stocks that was exchanged during the day), and it also has a value of zero for that day, meaning that nobody bought or sold the stocks on that day. And since the prices are prices of transactions (the first and the last one on a particular day, and the ones with the highest/lowest price), the prices cannot be established, and are irrelevant as there was not a single transaction on that day. Only the close price is assumed equal to its previous day counterpart because this is the most important value serving as a basis to determine the daily price change (and we assume no change in this case). Continuous-line charts also use this single value. Bar and candle charts usually display a blank space for a day where no trade occurred. "Almost every online datasources provide historical prices on given company / index's performance; from this, you can easily calculate ""standard deviation"" by yourself. With that said, standard deviation presumes a fixed set of data. Most public corporations have data spanning multiple decades, during which a number of things have changed: For these reasons, I have doubts on simplistic measures, such as ""standard deviation"" measuring any reality on the underlying vehicle. Professional investors usually tend to more time-point data, such as P/E ratio." "http://www.interactivedata.com -&gt; reference data  No, it's not free. Nor would I consider it ""high quality"".  For free data, try the Yahoo Finance API.  The data you want is there, though you may need to calculate some of the fields yourself.  Once you have your application working with free data you will be in a good position to evaluate whether it's worth it to shift to more detailed non-free data." There are several problems with trying to get this data: Robert Shiller published US Stock Market data from 1871.  Ken French also has historical data on his website.  Damodaran has a bunch of historical data, here is some historical S&P data. The closest I can think of from the back of my head is http://finviz.com/map.ashx, which display a nice map and allows for different intervals. It has different scopes (S&P500, ETFs, World), but does not allow for specific date ranges, though. On Monday, the 27th of June 2011, the XIV ETF underwent a 10:1 share split. The Yahoo Finance data correctly shows the historic price data adjusted for this split.  The Google Finance data does not make the adjustment to the historical data, so it looks like the prices on Google Finance prior to 27 June 2011 are being quoted at 10 times what they should be.   Coincidentally, the underlying VIX index saw a sudden surge on the Friday (24 June) and continued on the Monday (27 June), the date that the split took effect.  This would have magnified the bearish moves seen in the historic price data on the XIV ETF. Here is a link to an article detailing the confusion this particular share split caused amongst investors.  It appears that Google Finance was not the only one to bugger it up.  Some brokers failed to adjust their data causing a lots of confusion amongst clients with XIV holdings at the time. This is a recurring problem on Google Finance, where the historic price data often (though not always) fails to account for share splits. "In the US, stocks are listed on one exchange but can be traded on multiple venues.  You need to confirm exactly what your data is showing: a) trades on the primary-listed exchange; or b) trades made at any venue. Also, the trade condition codes are important.  Only certain trade condition codes contribute towards the day's open/high/low/close and some others only contribute towards the volume data.  The Consolidated Tape Association is very clear on which trades should contribute towards each value - but some vendors have their own interpretation (or just simply an erroneous interpretation of the specifications). It may surprise you to find that the majority of trading volume for many stocks is not on their primary-listed exchange.  For example, on 2 Mar 2015, NASDAQ:AAPL traded a total volume across all venues was 48096663 shares but trading on NASDAQ itself was 12050277 shares. Trades can be cancelled.  Some data vendors do not modify their data to reflect these busted trades.   Some data vendors also ""snapshot"" their feed at a particular point in time of the data.  Some exchanges can provide data (mainly corrections) 4-5 hours after the closing bell.  By snapshotting the data too early and throwing away any subsequent data is a typical cause of data discrepancies.   Some data vendors also round prices/volumes - but stocks don't just trade to two decimal places. So you may well be comparing two different sets of trades (with their own specific inclusion rules) against the same stock.  You need to confirm with your data sources exactly how they do things. Disclosure: Premium Data is an end-of-day daily data vendor." I couldn't find historical data either, so I contacted Vanguard Canada and Barclays; Vanguard replied that  This index was developed for Vanguard, and thus historical information is available as of the inception of the fund. Unfortunately, that means that the only existing data on historical returns are in the link in your question. Vanguard also sent me a link to the methodology Barclay's uses when constructing this index, which you might find interesting as well.  I haven't heard from Barclays, but I presume the story is the same; even if they've been collecting data on Canadian bonds since before the inception of this index, they probably didn't aggregate it into an index before their contract with Vanguard (and if they did, it might be proprietary and not available free of charge). There are several Excel spreadsheets for downloading stock quotes (from Yahoo Finance), and historical exchange rates at http://investexcel.net/financial-web-services-kb I don't see it in any of the exchange feeds I've gone through, including the SIPs. Not sure if there's something wrong with Nasdaq Last Sale (I don't have that feed) but it should be putting out the exact same data as ITCH.