[R] PLSR: model notation and reliabilities
I.Ioannou
r at roryt.gr
Sat Aug 27 03:04:13 CEST 2005
I'm new in both R and statistics. I "did my homework",
I tried the archives and whatever I managed to get
from the sources, but still I need assistance with
the plsr package.
I have a model with 2 core determinants D1 and D2,
made by 3 indicators each (D1a,D1b,D1c and so on).
Also I have 2 moderating variables (m1,m2), where
m1 moderates D1 and m2 modarates D2.
The dependent variable (Y) is also constructed by 3
indicators (Y1,Y2,Y3). Actually my model is far more
complicated, I just give a simplified example here.
Which is the correct notation for the model
(I'm skipping the crossvalidation for the moment) :
MyModel <- plsr(Y1+Y2+Y3 ~ ((D1a+D1b+D1c)*m1) + ((D2a+D2b+D2c)*m2),ncomp=2)
or :
Y <- cbind(Y1,Y2,Y3)
X1 <- cbind(D1a,D1b,D1c)
X2 <- cbind(D2a,D2b,D2c)
MyModel <- plsr( Y ~ (X1*m1) + (X2*m2),ncomp=2)
How do I calculate the internal composite reliabilty (ICR) ?
Is the Average variable explained (AVE) the mentioned as
"% variance explained" in summary ?
I tried something like (the model is the first notation
mentioned above, and the calcualtions below are simplified
just for clarity) :
ncomp=MyModel$ncomp
P <- MyModel$loadings[,ncomp]
Q <- MyModel$Yloadings[,ncomp]
# D1
f1 <- P["D1a"]
f2 <- P["D1b"]
f3 <- P["D1c"]
Sp <- f1 + f2 + f3
Sp2 <- (f1 ^ 2) + (f2^ 2) + (f3^2)
Sth <- (1-(f1 ^ 2)) + (1-(f2 ^ 2)) + (1-(f3^2))
D1_ICR <- (Sp^2) / ( (Sp^2) + Sth)
D1_AVE <- Sp2 / ( Sp2 + Sth)
but the results does not seem to give me something meaningfull.
For example, while cronbach(cbind(D1a,D1b,D1c)) gives me > 0.90,
the above computed D1_ICR gives me very low numbers (< .20).
Also summary says % variance explained for X = 83.1 in 1st component
while my computed D1_AVE is unacceptable (< 10%).
Where I made it wrong ? Or it is just my data ?
Any help will be much appriciated
TIA
More information about the R-help
mailing list