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There are plenty of quality
issues with software that downloads from
Yahoo including:
<SPAN
class=765494513-06082004>1. Significant inaccuracies
for any stock exchange that trades in increments less than 1c. This
includes the Australian Stock Exchange (ASX), Singapore Exchange, some NASDAQ
stocks and most OTCBB & Pink Sheet stocks. This happens because
Yahoo's data is rounded to the nearest cent. For example, there are 14000
listed instruments on the ASX. Over 8000 of them are currently trading
below 20c which means they move in either 0.5 or 0.1c increments. Since
Yahoo only prices in cents this introduce VERY SIGNIFICANT innacuracies. -
eg. a 2.6c shown as 3c represents a 15% error).
<SPAN
class=765494513-06082004>2. Normal dividends are
adjusted by subtracting all historical data by the dividend amount.
Exchanges such as the ASX do not adjust price data for standard dividends.
By diluting it the way they do, any technical analysis or backtesting no longer
shows a correct % return, nor does it show a critical technical levels such as
support and resistance.
<SPAN
class=765494513-06082004>3. No sector information -
critical if you want to perform sector-based analysis.
<SPAN
class=765494513-06082004>4. Significant number of
missing stock splits and other capital adjustments.
<SPAN
class=765494513-06082004>5. No delisted history - any
system testing you do based on Yahoo data is subject to population bias.
ie you can only test on the stocks that are currently
listed.
6. There is no
guarantee that Yahoo will continue to supply data, especially to automated
download programs. In Yahoo's Terms of Service, they have a clause which
says "You agree not to reproduce, duplicate, copy, sell, trade, resell or
exploit for any commercial purposes, any portion of the Service (including your
Yahoo! I.D.), use of the Service, or access to the Service.". Companies
that produce Yahoo downloaders are effectively exploiting the Yahoo service and
are therefore in breach of the Yahoo Terms of Service and Yahoo may shut down
these types of automated Yahoo downloading programs very easily.
So, whilst the Yahoo data is free to
obtain from the Yahoo site, you need to determine what you really need from the
data. If you're every likely to want to view historical charts (eg for
system development / backtesting / historical interest) then the old adage "you
get what you pay for" certainly applies here.
The best analogy I can use for data
feeds is they are like a game of Chinese Whispers. <A
href=""><FONT face=Arial
size=2>http://www.chinesewhispers.com/chinesewhispers.php<FONT
face=Arial size=2> In the case of programs that extract data from
Yahoo, the exchange sends data to Reuters. Reuters interpret the data, put
it into their databases, then take an extract of the data and send it to
Yahoo. Yahoo interprets the data, puts it into their database, then
extracts it onto the Yahoo Finance web site. Then the downloading program
obtains data from the Yahoo site, interprets it, and puts it onto the user's
PC. If at any step of the above process, the interpretation is slightly
incorrect then you have a discrepancy between actual events on the market and
data you receive. This is clearly the case with <SPAN
class=765494513-06082004>Yahoo downloader products out
there.
<SPAN
class=765494513-06082004>
Anyway,
please understand what you are receiving with these products and assess whether
these issues affect your trading system development, analysis or
interpretation.
<SPAN
class=765494513-06082004><SPAN
class=765494513-06082004>
Best regards,
Richard Dale.
Norgate Investor Services- Premium
quality Stock, Futures and Foreign Exchange Data for markets in
Australia, Asia, Canada, Europe, UK & USA -<A
title=http://www.premiumdata.net/ href=""><FONT
face=Arial size=2>www.premiumdata.net
From: MJ Jossart
[mailto:mj008867@xxxxxxxxxxxxxxxxx] Sent: Friday, 6 August 2004 7:36
PMTo: Metastockusers@xxxxxxxxxxxxxxxSubject: Re:
[Metastockusers] I Search a speed downloader for Yahoo historical
!
I asked the same kind of question in the
EquisMetastock Yahaoo group. I guess this would no problem if the
Equis Downloader can support multiple configurations, ... is it so
?
----- Original Message -----
<BLOCKQUOTE dir=ltr
>
<DIV
>From:
David
Linton
To: <A
title=Metastockusers@xxxxxxxxxxxxxxx
href="">Metastockusers@xxxxxxxxxxxxxxx
Sent: Thursday, August 05, 2004 11:08
PM
Subject: Re: [Metastockusers] I Search a
speed downloader for Yahoo historical !
<FONT face=Arial
color=#0000ff size=2>
Would I have problems continuing with the Reuters
feed for stocks (to ensure data accuracy, splits, new symbols, etc) but using
the Hyper Trader Smart Downloader for free Yahoo indices and futures
data?
Thanks for your advice.
David
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