On Thu, 28 Jul 2022 00:42:51 +0000 "Ebert,Timothy Aaron" <teb...@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. cheers, Rolf 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? R. -- Honorary Research Fellow Department of Statistics University of Auckland Phone: +64-9-373-7599 ext. 88276 ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
