Strange values in ARM.L price data 1998-2000 from Yahoo
This is just a shot in the dark but it could be intermarket data. If the stock is interlisted and traded on another market exchange that day then the Yahoo Finance data feed might have picked up the data from another market. You'd have to ask Yahoo to explain and they'd have to check their data.
In less than two decades, more than half of all publicly traded companies have disappeared. There were 7,355 U.S. stocks in November 1997, according to the Center for Research in Security Prices at the University of Chicago’s Booth School of Business. Nowadays, there are fewer than 3,600.  A close look at the data helps explain why stock pickers have been underperforming. And the shrinking number of companies should make all investors more skeptical about the market-beating claims of recently trendy strategies.  Back in November 1997, there were more than 2,500 small stocks and nearly 4,000 tiny “microcap” stocks, according to CRSP. At the end of 2016, fewer than 1,200 small and just under 1,900 microcap stocks were left.  Most of those companies melted away between 2000 and 2012, but the numbers so far show no signs of recovering.  Several factors explain the shrinking number of stocks, analysts say, including the regulatory red tape that discourages smaller companies from going and staying public; the flood of venture-capital funding that enables young companies to stay private longer; and the rise of private-equity funds, whose buyouts take shares off the public market.  For stock pickers, differentiating among the remaining choices is “an even harder game” than it was when the market consisted of twice as many companies, says Michael Mauboussin, an investment strategist at Credit Suisse in New York who wrote a report this spring titled “The Incredible Shrinking Universe of Stocks.”  That’s because the surviving companies tend to be “fewer, bigger, older, more profitable and easier to analyze,” he says — making stock picking much more competitive.  Consider small-stock funds. Often, they compare themselves to the Russell 2000, an index of the U.S. stocks ranked 1,001 through 3,000 by total market value. “Twenty years ago, there were over 4,000 stocks smaller” than the inclusion cutoff for the Russell 2000, says Lubos Pastor, a finance professor at the University of Chicago. “That number is down to less than 1,000 today.”  So fund managers have far fewer stocks to choose from if they venture outside the index — the very area where the best bargains might be found. More money chasing fewer stocks could lead some fund managers to buy indiscriminately, regardless of value.  Eric Cinnamond is a veteran portfolio manager with a solid record of investing in small stocks. Last year, he took the drastic step of shutting down his roughly $400 million mutual fund, Aston/River Road Independent Value, and giving his investors their money back.  “Prices got so crazy in small caps, I fired myself,” he says. “My portfolio was 90% in cash at the end, because I couldn’t find anything to buy. If I’d kept investing, I was sure I’d lose people their money.”  He adds, “It was the hardest thing I’ve ever done professionally, but I didn’t feel I had a choice. I knew my companies were overvalued.”  Mr. Cinnamond hopes to return to the market when, in his view, values become attractive again. He doesn’t expect recent conditions to be permanent.  The evaporation of thousands of companies may have one enduring result, however — and it could catch many investors by surprise.  Most research on historical returns, points out Mr. Mauboussin, is based on the days when the stock market had twice as many companies as it does today. “Was the population of companies so different then,” he asks, “that the inferences we draw from it might no longer be valid?”  So-called factor investing, also known as systematic or smart-beta investing, picks hundreds or thousands of stocks at a time based on common sources of risk and return. Among them: how big companies are, how much their shares fluctuate, how expensive their shares are relative to asset value and so on.  But the historical outperformance of many such factors may have been driven largely by the tiniest companies — exactly those that have disappeared from the market in droves.  Before concluding that small stocks or cheap “value” stocks will outrace the market as impressively as they did in the past, you should pause to consider how they will perform without the tailwinds from thousands of tiny stocks that no longer exist.  The stock market has more than tripled in the past eight years, so the eclipse of so many companies hasn’t been a catastrophe. But it does imply that investing in some of the market’s trendiest strategies might be less profitable in the future than they looked in the past. In general, the short answer is to use SEDAR, the Canadian database that compiles financial statements for Canadian companies. The financial statements for Pacific Rubiales Energy Corp can be found here.  The long answer is that the data might be missing because in Canada, each province has their own agency to regulate securities. Yahoo might not compile information from such a wide array of sources. If other countries also have a decentralized system, Yahoo might not take the time to compile financial information from all these sources. There are a myriad of other reasons that could cause this too, however.  This is why SEDAR is useful; it 's the Canadian equivalent of the SEC's EDGAR database, and it maintains a sizeable database of financial statements. Should be noted that pacoverflow's answer is wrong. Yahoo back-adjusts all the previous (not current or future) values based on a cumulative adjustment factor. So if there's a dividend ex-date on December 19, Yahoo adjusts all the PREVIOUS (December 18 and prior) prices with a factor which is: 1 - dividend / Dec18Close "Generally, ETFs work on the basis that there exists a pair of values that can be taken at any moment in time: A Net Asset Value of each share in the fund and a trading market price of each share in the fund.  It may help to picture these in baskets of about 50,000 shares for the creation/redemption process. If the NAV is greater than the market price, then arbitrageurs will buy up shares at the market price and do an ""in-kind"" transaction that will be worth the NAV value that the arbitrageurs could turn around and sell for an immediate profit. If the market price is greater than the NAV, then the arbitrageurs will buy up the underlying securities that can be exchanged ""in-kind"" for shares in the fund that can then be sold on the market for an immediate profit. What is the ETF Creation/Redemption Mechanism? would be a source on this though I imagine there are others. Now, in the case of VXX, there is something to be said for how much trading is being done and what impact this can have. From a July 8, 2013 Yahoo Finance article: At big option trade in the iPath S&P 500 VIX Short-Term Futures Note   is looking for another jump in volatility.  More than 250,000 VXX options have already traded, twice its daily   average over the last month. optionMONSTER systems show that a trader   bought 13,298 August 26 calls for the ask price of $0.24 in volume   that was 6 times the strike's previous open interest, clearly   indicating new activity. Now the total returns of the ETF are a combination of changes in share price plus what happens with the distributions which could be held as cash or reinvested to purchase more shares." "This company was a reputable rating agency for many years. See Weiss Research website, ratings section for a very different perspective on Martin Weiss's work than the websites with which he is now associated. I checked both links provided, and agree with the questioner in every way: These appear to be highly questionable investment research websites. I use such strong terms based on the fact that the website actually uses the distasteful pop-up ploy,  ""Are you SURE you want to leave this site?"" Clearly, something changed between what Weiss Ratings was in the past (per company history since 1971) and what Martin Weiss is doing now. Larry Edelson seems to have been associated exclusively with questionable websites and high pressure investment advice since 2007. From 1996 through the present, he worked as either an employee or contractor of Weiss Research. Let's answer each of your questions.  On June 22, 2006, the Commission instituted settled administrative   proceedings against Weiss Research, Inc., Martin Weiss, and Lawrence   Edelson (collectively, “Respondents”) for violations of the Investment   Advisers Act of 1940 in connection with their operation of an   unregistered investment adviser and the production and distribution of   materially false and misleading marketing materials. Full details about Weiss Ratings operations, including its history from 1996 through 2001, when it operated in compliance with securities laws, then from 2001 through 2005, which was when the SEC filed charges for regulatory violations, are available from the June 2006 U.S. SEC court documents PDF. Finally, this quantitative assessment, ""Safe With Martin Weiss? (December 2010) by CXO Advisory (providers of ""objective research and reviews to aid investing decisions"") for its readers concluded the following: In summary, the performance of Martin Weiss’ premium services in   aggregate over the past year is unimpressive. The study methodology was good, but I recommend reading the article (I posted the URL) to fully understand what caveats and assumptions were done to reach that conclusion." IESC has a one-time, non-repeatable event in its operating income stream.  It magnifies operating income by about a factor of five.  It impacts both the numerator and the denominator.  Without knowing exactly how the adjustments are made it would take too much work for me to calculate it exactly, but I did get close to their number using a relatively crude adjustment rule. Basically, Yahoo is excluding one-time events from its definitions since, although they are classified as operating events, they distort the financial record.  I teach securities analysis and have done it as a profession.  If I had to choose between Yahoo and Marketwatch, at least for this security, I would clearly choose Yahoo. Robert Shiller has an on-line page with links to download some historical data that may be what you want here. Center for the Research in Security Prices would be my suggestion for another resource here. On 2012/05/18 at 15:34:00 UTC (11:34:00 EDT) FB was in chaos mode.  The most recent public US trade at that moment was at $40.94, but in the next one second (i.e. before the clock hit 15:34:01) there were several dozen trades as low as $40.76 and as high as $41.00. On 2012/05/30 at 17:21:00 UTC (13:21:00 EDT) the most recent public US trade for FB was at $28.28.