Grass {candisc} | R Documentation |
The data frame Grass
gives the yield (10 * log10 dry-weight (g))
of eight grass Species in five replicates (Block) grown in sand culture
at five levels of nitrogen.
data(Grass)
A data frame with 40 observations on the following 7 variables.
Species
B.media
D.glomerata
F.ovina
F.rubra
H.pubesens
K.cristata
L.perenne
P.bertolonii
Block
1
2
3
4
5
N1
N9
N27
N81
N243
Nitrogen (NaNO3) levels were chosen to vary from what was expected to be from critically low to almost toxic. The amount of Nitrogen can be considered on a log3 scale, with levels 0, 2, 3, 4, 5. Gittins (1985, Ch. 11) treats these as equally spaced for the purpose of testing polynomial trends in Nitrogen level.
The data are also not truly multivariate, but rather a split-plot experimental design. For the purpose of exposition, he regards Species as the experimental unit, so that correlations among the responses refer to a composite representative of a species rather than to an individual exemplar.
Gittins, R. (1985), Canonical Analysis: A Review with Applications in Ecology, Berlin: Springer-Verlag, Table A-5.
str(Grass) grass.mod <- lm(cbind(N1,N9,N27,N81,N243) ~ Block + Species, data=Grass)