1 Reply Latest reply on Dec 27, 2011 10:29 PM by Richard Leeke

    Reference line for stdev not behaving as expected

    Ya'ir Aizenman

      Hi Folks,

       

      Attached is a simple plot of mine showing a timeseries, with reference lines for the historical average and the historical stddev ("-1,1 standard deviation").

       

      What confuses me though is that the stdev band is about half what I would expect it to be.  The width of the band is: 3.934 - 3.416 = 0.518.  But as you can see by the graph on the bottom the stddev NEVER goes below 0.6 (in fact, the stddev is 0.940 over 422 data points).

       

      Does anyone understand how tableau is doing this calculation?

       

      Thanks,

      Y