Dear All,
I am a researcher doing research in plant growth and I have a
statistical problem that seems to not be able to handle. Recently, I
conducted an experiment about plant growing in three different
nutrient-level sediments. I harvested these every three week (three
harvests in all). Some growth traits of these plants were recorded (e.g.
total biomass, leaf biomass and stem biomass). In addition, I found that
the total plant biomass may also influence these traits. So, I am going
to use total biomass as covariate to do the statistical analysis.
Meanwhile, this experimental design is repeated design, I guess I have
to do the repeated-measurement (repeated measure ANCOVA with varying
covariate) to analyze the growth traits between different
nutrient-levels. I've tried gls and lme function with a correlation
structure applied to time series in nlme library with great help by Dr.
Yuanye Zhang. However, I still can't figure out the "between-subject"
and "with-subject" parts.
Do you know if R can do repeated measures ANCOVA with varying covariate?
if yes how?
Thanks for any help. Much appreciated.
Dong Xie
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