SPY 200 Day Moving Average Discrepancy

Yesterday I commented that SPY bounced on nothing in the past 2 days.   Price pierced through tradestation’s 200 day EMA.  By chance I looked at stockcharts.com’s SPY daily chart and my eyes popped out because on that chart, SPY bounced exactly at the 200 day EMA!!!

So I began “debugging” the problem.  I found that 20 day MA’s (regardless of simple or exponential) are identical between the two.  50 day MA’s are only slightly off.  But 200 MA’s are about way off, like almost $1 !

I then looked at the historic data and discovered that after 9/15/11, the data points are identical, but prior to (and including) tbat date, stockcharts.com’s SPY closing price are consistently about $.60 lower!!

I resort to a third party, yahoo.com, for sanity check.  I found that yahoo.com’s data matches that of tradestation (which is the one I use).   And in the process I found the culprit:  SPY paid out dividends in the amount of $.625 on 9/16/11  !!

But still, who’s data is right and who’s is wrong?   Given that SPY bounced off stockcharts.com’s 200 day EMA in the past 2 days, either stockcharts.com is right, or the majority of traders use stockcharts.com even if its data is wrong.    Isn’t that how the English grammar works also?    Enough people doing it wrong makes it right.

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