On Nov 25, 2011, at 2:56 PM, magushi wrote:
> Hi every one.
> I want to analyze my data. The y (density) is very skewed to the
> right.
> this is my tentative fit<-density~factor(Site)+factor(Species)+ depth.
> which model to apply between glm and lm, for sure I can not use
> lm( This is
> non linear data)
Until you have looked more carefully at your tentative fit you are
jumping to unsupported assumptions. It is a common misconception that
a skewed distribution of the dependent variable represents a problem
for linear methods. It may be true but you will not know until you
look at the distribution of the residuals of a linear fit. So far we
see not evidence that you have done so. If you showed us plots of
density ~ depth within categories of Site and Species then there might
be a basis for discussion of alternative links or transformations.
This wouldn't be homework by any chance, would it?
>
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David Winsemius, MD
West Hartford, CT