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  ASReml  ~  Doubly multivariate analysis with ASREML-R 4.1

Posted: Mon Nov 25, 2019 7:08 pm Reply with quote
Joined: 15 Nov 2019 Posts: 1
Good day:

I have a doubly multivariate dataset that consists of root length data at 4 depths, captured over time during two growing seasons. This is superimposed on a split-plot design where CO2 concentration is the main plot, and cultivar is the subplot. I have been able to analyse the aggregated root length over time, and I have analysed each date separately as a typical repeated measure with ASREML-R 4.1. However, it looks like the two cultivars do show differences in root length distribution over time, and I'm not capturing this with analyses over separate samplings. I would like to analyse this with the entire data set if possible.

Some of the issues I am running into is
1) the software doesn't seem to like it when I use the time factor (days after planting) as a numerical value. When I use this in the residual, I get an error message that says "Error in spc("cor", "cor", 0.1, numeric(0), NA, obj, init, data) : DAP must be a factor".
2)At the moment, I'm only using the DAP correlation in the residual term, but I'm not sure if I should have the Depth too?
3) I have a lot of zeros, especially at the beginning of the season as roots have not yet grown into the deeper layers. Could that be a problem? My residuals plots sure look funky.
4) Since this is a growth curve, I was thinking of using a power error structure, however, regardless of the correlation error structure, I always get the same loglikelihood and residuals plots. Is that normal?

Any advice?
Thanks in advance,
Maryse B
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