This might be embarrasingly easy or impossible; I've been a computer programmer for too long since my statistics classes to tell for sure(adsbygoogle = window.adsbygoogle || []).push({});

I have a set of records with the following data for each record: interval, mean speed, standard deviation of speed, number of observations. Exempli gratia:

Now, if I want to aggregate the data to get mean speed and standard deviation over two or more intervals (1 and 2 above), calculating the weighted mean is no problem but how - if possible - do I calculate the standard deviation for the aggregated intervals?Code (Text):1, 77.2, 1.75, 10

2, 75.9, 2.05, 12

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# Standard deviation of aggregated data

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