7 Replies Latest reply on Dec 1, 2013 9:33 AM by Robert Morton

    Negative variance problem with large dataset, bug?

    Chris Love

      Hi all,

       

      I'm having a problem creating a variance across a large dataset. I've replicated this with some data I can share by creating a 50 million recordset and attaching a random value between 0 and 100,000 and shared the workbook on dropbox.

       

      https://dl.dropboxusercontent.com/u/30680444/Variance%20Problem.twbx

       

      I want to find the variance of the Value. So I'm using a calculation.

       

      Var([Value])

       

      The result is a negative variance, which is impossible.

       

      I think the problem is that the values are too big and the sum of the squares in the variance calculation is just looping back round to negative in Tableau, can anyone take a look and confirm I'm not doing anything wrong? The calculation works on smaller values.

       

      Also how do I report a bug, assuming this is one?

       

      Kind Regards,

      Chris