We get this question a lot about why results folks find here are different than on other web sites. Basically it comes down to two things: computation and data.
In regards to computation you can come up with a different results for the same computation based on the kinds of assumptions you make in your calculation. What window length, how many standard deviations, what did you use for the risk free rate, log returns or raw returns, are just a few examples of assumptions made explicitly or implicitly when making computations. Furthermore you can see that even financial data providers like Yahoo or Google have discrepancies between their metrics. See this thread for some information (albeit old) related specifically to MACD calculations on Quantopian, Yahoo, Google.
It is probably worth mentioning that another major difference is the type of data we use, vs others. Straight from the FAQ...
Quantopian uses the last traded price as the close price for the
security. Depending on the data source, others may use end-of-day
(EOD) prices. For example, Yahoo is an EOD datasource. Yahoo and other
EOD data providers get their price and volume data from the official
exchange record. Quantopian's data is generated by the actual trades,
regardless of what exchange the trade was made on. The EOD sources
rarely exactly match data derived from intraday data. For instance,
the official close for a NYSE stock is the last trade of the day for
the stock on NYSE. But if the stock also trades on Chicago, Pacific or
another regional exchange, the last trade on one of those exchanges
could be our close.
You can read more here. That should shine some light onto why you are seeing different results.
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