Dear R community,
I am trying to do a split-plot analysis as follows. I have a data set
(?morf?) with plant data from 6 ?blocks? at different latitudes, each
divided in 3 plots. The full-plot ?treatment? is ?soil type? and has
three levels. Within each plot I have two levels of radiation, coded as
?SUN? and ?SHADE?. I have data for several response traits for 30 plants
within each subplot, that is 1080 plants in total (6 Blocks x 3Plots x
2Radiation levels x 30 Plants).
I want to measure a) if there are differences between latitudes
(?blocks?) and b) how these differences interact with radiation levels.
I am not so interested in the effect of soil type, which I already know,
but radiation effects depend on soil type. The model I?m looking for
should look something like:
Response ~ Block*Radiation | Soil type
I have tried to use lme. The basic formulation I have tried is:
lme(Resp~Block*Radiation, random=~ 1 | Plot/Radiation, data=morf)
but I keep on getting the error message:
?Error in getGroups.data.frame(dataMix, groups) : Invalid formula for
groups?
I don?t know why this is happening, could it be because ?Radiation? has
only two levels? I don't have missing values or any other obvious source
of "noise"
Since neither lme nor lmer weren?t working, I tried ?aov?. I played
around a bit with the "Oats" data set and saw that:
aov( yield ~ ordered(nitro) * Variety + Error(Block/Variety), data = Oats)
gives the same results as the standard
lme( yield ~ ordered(nitro) * Variety, data = Oats, random = ~ 1 |
Block/Variety )
So I used the following formulation
aov(Resp~Block*Radiation+Error(Plot/Radiation), data=morf)
This seems to work fine, but I am not that confident I am using the
correct syntax.
Any advice and/or guidance would be much appreciated.
Thank you in advance.
RAFA
