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GEOSTATS: log SD

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  • Milo Simonic
    I am interested on opinions on how to treat log tranformed data. I am working with water quality data - trying to characterize the regions nationwide by some
    Message 1 of 1 , Jan 25, 1999
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      I am interested on opinions on how to treat log tranformed data. I am
      working with water quality data - trying to characterize the regions
      nationwide by some single central values. I use geometric mean,
      calculated from log data as an "average" value. With log data there are
      however problems such as the following:

      1. What is the equivalent of standard deviation on log transformed
      dataset (especially when it comes to back-transforming)? What I did was
      to calculate the "normalized standard deviation", which was SD of log
      data divided by mean of log data. However I do need some "spread"
      parameter in absolute numbers for a general public.The workaround by
      using range defined between two back-transformed SD (derived from log
      data) seems to be too speculative and non-intuitive to me.

      2. While log transforming data, values less than 1 return negative
      values. How to deal with this situation?

      Thanks for useful replies,

      Milo Simonic
      Hydromedia Solutions
      South Africa


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