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Re: AI-GEOSTATS: Log transformation and zeros

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  • Brian R Gray
    while possibly outside the domain of your original question, I suspect that you may be able to treat your yield data as integers by treating the denominator as
    Message 1 of 8 , Oct 3, 2002
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      while possibly outside the domain of your original question, I suspect that
      you may be able to treat your yield data as integers by treating the
      denominator as an offset variable (as a technicality, I'd argue that, even
      after dividing by a constant, your data remain discrete--just not
      integers). this common technique would appear to take you back into the
      discrete world that Nicholas touched on. brian

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      Brian Gray
      USGS Upper Midwest Environmental Sciences Center
      575 Lester Avenue, Onalaska, WI 54650
      ph 608-783-7550 ext 19, FAX 608-783-8058
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      Ernesto Jardim
      <ernesto@ipimar. To: Nicholas Lewin-Koh <nikko@...>
      pt> cc: Mailing List AI-Geostats <ai-geostats@...>
      Sent by: Subject: Re: AI-GEOSTATS: Log transformation and zeros
      ai-geostats-list
      @...


      10/02/2002 09:47
      AM
      Please respond
      to Ernesto
      Jardim





      Hi

      The data are not discrete. We collect number per hour, so it's a yield !

      Thanks

      EJ

      On Wed, 2002-10-02 at 15:27, Nicholas Lewin-Koh wrote:
      > Hi,
      > If the data are counts, ie integer number of fish and not tons, you
      > might want to try a discrete model such as a negative binomial or
      > Poisson. I have listed some references below, the top two have a more
      > Bayesian flavor.
      >
      > Nicholas
      >
      >
      > Alexander, N., Moyeed, R., Stander, J. (2000). Spatial modelling of
      > individual-level parasite counts using the negative binomial
      > distribution, Biostatistics, 2000, 1, 453-463.
      >
      > Diggle, P. J., Moyeed, R. A., Tawn, J. A. (1998). Model-based
      > geostatistics (with discussion), J. R. Statist. Soc. C, 47, 299-350.
      >
      > Gotway, C.A., Stroup, W.W. (1997) A Generalized Linear Model Approach
      > to Spatial Data Analysis and Prediction. Journal of Agricultural, Bio-
      > logical and Environmental Statistics 2(2), pp. 157­178.
      >
      >
      > On Wed, 2002-10-02 at 19:24, Ernesto Jardim wrote:
      > > Hi
      > >
      > > I'm analysing fisheries data (number of fish caught per hour) and I
      have
      > > some 0 values. When I log-trans I have to translate the values by
      hading
      > > some value.
      > >
      > > My question is which value is the best ? is there any works about this
      ?
      > >
      > > I usually had 1 so that I get values between 0 and infinite (no
      negative
      > > value) but I have doubts about it.
      > >
      > > Regards
      > >
      > > EJ
      > >
      > >
      > >
      > >
      > > --
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      >



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