[R] Predicted values from glm() when linear predictor is NA.

Rolf Turner r@turner @end|ng |rom @uck|@nd@@c@nz
Thu Jul 28 04:09:30 CEST 2022

On Thu, 28 Jul 2022 00:42:51 +0000
"Ebert,Timothy Aaron" <tebert using ufl.edu> wrote:

> Time is often used in this sort of problem, but really time is not
> relevant. A better choice is accumulated thermal units. The insect
> will molt when X thermal units have been accumulated. This is often
> expressed as degree days, but could as easily be other units like
> degree seconds. However, I suspect that fine time units exceeds the
> accuracy of the measurement system. A growth chamber might maintain
> 28 C, but the temperature the insect experiences might be somewhat
> different thereby introducing additional variability in the outcome.
> No thermal units accumulated, no development, so that is not an
> issue. This approach allows one to predict life stage over a large
> temperature range. Accuracy can be improved if one knows the lower
> development threshold. At high temperatures development stops, and a
> mortality function can be added.

Very cogent comments in respect of dealing with the underlying
practical problem, but I am not so much concerned with the practical
problem at the moment but rather with the workings of the software that
I am using.



P.S.  I am at several removes from the data set(s) that I am messing
about with.  But if my understanding is correct (always an assumption
of which to be sceptical!) these data were collected with the
temperature being held *constant*, whence time and accumulated thermal
units would be equivalent.  Is it not so?


Honorary Research Fellow
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

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