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Recently I've started gathering some end-of-day (EOD) prices data for my testing. The first obvious place where such data is freely available is Yahoo Finance site. However I've noticed that many data providing companies sell this data, and not so cheap. So my question is: why would anyone purchase this data if it is freely available on Yahoo? One of my assumptions would be the data packaging (as Yahoo only allows you to download the data file-by-file) but then there are dozens of downloaders freely available on the nets. So do I miss something? Is this Yahoo data not reliable enough?

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    More reliable sources of data that you might pay for cater for stock splits, mergers and other corporate actions. – Victor Apr 16 '13 at 11:08
  • I'm having the same problem, I'm tracking 30 stocks and have a "Portfolio" on Yahoo but they are taking a long time to show current closing price, sometimes close to midnight. Noticed the same problem with Marketwatch yesterday. – user19222 Jul 24 '14 at 4:02
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There are several reasons to pay for data instead of using Yahoo Finance, although these reasons don't necessarily apply to you if you're only planning to use the data for personal use.

  1. Yahoo will throttle you if you attempt to download too much data in a short time period. You can opt to use the Yahoo Query Language (YQL), which does provide another interface to their financial data apart from simply downloading the CSV files. Although the rate limit is higher for YQL, you may still run into it. An API that a paid data provider exposes will likely have higher thresholds.

  2. Although the reliability varies throughout the site, Yahoo Finance isn't considered the most reliable of sources. You can't beat free, of course, but at least for research purposes, the Center for Research in Security Prices (CRSP) at UChicago and Wharton is considered the gold standard. On the commercial side, data providers like eSignal, Bloomberg, Reuters also enjoy widespread popularity.

  3. Although both the output from YQL and Yahoo's current CSV output are fairly standard, they won't necessarily remain that way. A commercial API is basically a contract with the data provider that they won't change the format without significant prior notice, but it's reasonable to assume that if Yahoo wanted to, they could make minor changes to the format and break many commercial applications. A change in Yahoo's format would likely break many sites or applications too, but their terms of use do state that Yahoo "may change, suspend, or discontinue any aspect of the Yahoo! Finance Modules at any time, including the availability of any Yahoo! Finance Modules. Yahoo! may also impose limits on certain features and services or restrict your access to parts or all of the Yahoo! Finance Modules or the Yahoo! Web site without notice or liability."

  4. If you're designing a commercial application, a paid provider will probably provide technical support for their API.

  5. According to Yahoo Finance's license terms, you can't use the data in a commercial application unless you specifically use their "badges" (whatever those are). See here. In this post, a Yahoo employee states:

The Finance TOS is fairly specific. Redistribution of data is only allowed if you are using the badges the team has created.

Otherwise, you can use YQL or whatever method to obtain data for personal use.

The license itself states that you may not:

sell, lease, or sublicense the Yahoo! Finance Modules or access thereto or derive income from the use or provision of the Yahoo! Finance Modules, whether for direct commercial or monetary gain or otherwise, without Yahoo!'s prior, express, written permission

In short, for personal use, Yahoo Finance is more than adequate. For research or commercial purposes, a data provider is a better option. Furthermore, many commercial applications require more data than Yahoo provides, e.g. tick-by-tick data for equities, derivatives, futures, data on mergers, etc., which a paid data source will likely provide.

Yahoo is also known for inaccuracies in its financial statements; I can't find any examples at the moment, but I had a professor who enjoyed pointing out flaws in the 10K's that he had come across. I've always assumed this is because the data were manually entered, although I would assume EDGAR has some method for automatic retrieval. If you want data that are guaranteed to be accurate, or at least have a support contract associated with them so you know who to bother if it isn't, you'll need to pay for it.

  • Hi John and thank you for your answer. Actually I have already created a simple downloader and I was able to retrieve all symbols prices for NYSE and NASDAQ with no problems. I have also compared random periods of data with prices provided on some reputable sites (in my opinion, but I might be wrong) and it seemed pretty accurate. – Eugene S Apr 16 '13 at 3:44
  • And yes, I am using it for personal use ONLY. – Eugene S Apr 16 '13 at 3:45
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    Anecdotal evidence regarding the quality of Yahoo! Finance data: In 2006, after a 1:100 reverse stock split that Y! had overlooked, the apparent price of a GTL.L share jumped 100x. I reported this, and a few days later... all data from before the consolidation was just deleted. – aidan Apr 16 '13 at 6:38
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    @EugeneS The only time I've noticed reliability issues with Yahoo Finance has been in financial statements and occasionally options chains, but aidan's point is certainly more worrisome! – John Bensin Apr 16 '13 at 11:05
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    In my view, the # 1 flaw in Yahoo! finance data is that they add a column "Adjusted Close" to their historical data but while it is adjusted for dividends and splits, they do not adjust the other daily prices (Open, High, Low, Close) and daily volumes for splits. This creates a picture that is internally inconsistent. For example it is near impossible to figure out the dollar value volume of a day far in history because prices and volumes are not being split adjusted. – arielf Apr 3 '14 at 6:01

protected by Chris W. Rea Jul 4 '17 at 4:02

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