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STD function not accurate
Posted by: Y B
Date: April 02, 2016 03:09PM

Hi All,
The std function is very useful and I use it often. However, I noticed I am getting slightly different results compared to computing the standard deviation in R or Excel for the same values.

Here is my query:
select distinct stain, cell, organ, group_concat(value), avg(value), std(value) from mydata where bacteria="germ free" group by stain, cell, organ

Now here are the values from one row, from the group_concat field:
13.10000038,14,10.19999981,11.19999981,26.5,18.5,7.5,16.70000076,21.70000076,10.10000038,15.39999962,11.69999981,13.69999981,31.79999924,21.10000038,35.29999924,34.09999847,10.10000038,9.39999962,32.5,17.10000038,16.89999962,19.39999962,19.10000038,16.60000038,15.19999981,15.69999981,17.20000076,11.60000038,22.70000076,16.89999962,12.80000019

The mean is computed correctly and is: 17.68125001
The std is computed as: 7.260140888

However, when using these values in R or Excel, the std is: 7.376311

This seems like a big difference. Can anyone provide an explanation? I have been using the STD function for a while and now getting worried.

Thanks.

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STD function not accurate
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April 02, 2016 03:09PM
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April 02, 2016 08:23PM


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