[R-sig-ME] mixed model for nested factor?
jszhao at yeah.net
Tue May 9 04:25:17 CEST 2017
Thank you very much for the reply. The 2, 1 and 0 are not the amount of
warming. They are just codes for the warming strength. Since the warming
pattern is different in Spring and Fall, I wonder that warming pattern
(Temp) is nested in Season.
Another concern is how to deal with Year. I hope to test the time effect
on SOC. Should Year be treated as continuous variable or factor? I
recorded the exact time of soil sampling.
On 2017/5/9 2:35, Thierry Onkelinx wrote:
> Dear Jinsong,
> IMHO you want to detect a potential effect of warming. The amount of
> warming seems to be less relevant. Therefore I'd recode temperature into a
> factor with two levels: warming = yes and warming = no.
> Then add the interaction between warming and season to the model. That will
> take care of the difference in warming between spring and fall.
> Best regards,
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
> team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
> Kliniekstraat 25
> 1070 Anderlecht
> To call in the statistician after the experiment is done may be no more
> than asking him to perform a post-mortem examination: he may be able to say
> what the experiment died of. ~ Sir Ronald Aylmer Fisher
> The plural of anecdote is not data. ~ Roger Brinner
> The combination of some data and an aching desire for an answer does not
> ensure that a reasonable answer can be extracted from a given body of data.
> ~ John Tukey
> 2017-05-08 16:13 GMT+02:00 Jinsong Zhao <jszhao at yeah.net>:
>> Hi there,
>> We have conducted an experiments for five years. The experiment is a
>> completed block design with repeated measures. In detail, there is only one
>> factor, i.e., temperature, and the experiments is performed in four blocks.
>> In each block, the plot was split into two subplots. One subplot received
>> two degree warming in Spring, and one degree warming in Fall, the other
>> subplot didn't received any changes in Spring and Fall. We measured SOC
>> every Spring and Fall. So we have got data something like:
>> SOC, Temp, Season, Year, block
>> 2.032, 2, Spring, 2007, 1
>> 1.988, 0, Spring, 2007, 1
>> 1.977, 1, Fall, 2007, 1
>> 1.881, 0, Fall, 2007, 1
>> It seems that mixed model might be the right way to analyze the data.
>> However, we have encountered the difficulties that Temp seems to be nested
>> with Season, and don't know how to code a formula for lme() in nlme package.
>> Any suggestions or comments will be really appreciated. Thanks in advance.
>> Best regards,
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