[R-sig-ME] Understanding and analysing split split design using lmer()
kc000001 @end|ng |rom umn@edu
Mon Sep 9 20:35:18 CEST 2019
Hello R mixed models community,
I am trying to fit a model for a split- split-plot design using lmer. I
know how to do this with aov and ssp.plot function in agricolae, but I need
to use lmer in this case.
I am interested in the response variable biomass of cover crops. I have the
main plots as crops (corn and soybean). The subplot is tillage, which is
randomized within the crops and has 3 levels (conventional-till, no-till,
and strip-till). Within tillage(sub plot), 3 cover crop strategies are
randomly assigned (AR, ARCC, ARCCFR). Therefore 1 rep (block) has 18
treatments. The whole experiment is replicated 4 times, therefore, total
experimental units equal to 72 units.
Data arranged in a csv file is attached in this email.
Now the analysis part:
I know how to do this using aov/ ssp.plot( agricolae). The code is as
Same thing with aov:
For my analysis using lmer, and lme, I have the following code:
model3<-lme(fixed=biomass~crop*tillage*cover, data=data, random=~1|rep)
Now my confusion and questions are:
1. I have used crop, tillage, and cover as fixed effects. And only the rep
(block) as random. Is the random effect properly assigned for this design?
2. I have read a lot about crossed and nested design. Crawley and Oehlert
give particular examples about it, but I have trouble understanding if this
design has nested factors or crossed factors.
I would be very relieved to receive feedback with the matter in hand.
Looking forward, and thank you a lot,
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