1 Reply Latest reply on Jul 15, 2016 7:28 AM by jbante

    Standard deviation data set up for chart


      Hi there


      I'm looking to move data from Excel to FM and produce charts from it.  These charts will be the typical bell curves that a standard deviation range produces happily at the moment in Excel.


      I'm having a couple of issues around the NORMDIST and STDEV(p) calculations.  I should also add at this point I am certainly no mathematician!!


      I've set up a table to test with which simply has 4 fields:


      • dData - the data values which are sorted low to high
      • cDistribution - is a calculation field which uses the custom function from here : FileMaker Custom Function:_Normsdist ( z )
      • cAverage - A native summary (average) calculation
      • cStdDev - A native calculation StDev (dData) <<< I think this needs another parameter, but not sure


      I've set things up this way as it matches what I've done on Excel and when the results are plotted I get a lovely smooth curve.


      I can plot the results on here, but the values differ somewhat from Excel and the curve is far from smooth as a result.


      Appreciate any help on this.



        • 1. Re: Standard deviation data set up for chart

          It looks like the function you link to is using an approximation to the Normal CDF. If Excel is using an exact calculation, the results will of course be a little different, especially at the extremes; but they shouldn't be a lot different. Here's my version of the same function, which appears to be using a different approximation. Maybe it works better for you.


          If you can post a sample file, that would help us better see what you're seeing.


          The StDev function does not need another parameter. It's also available as a summary field type, if you want to be consistent with your cAverage field.