library(chemCal)
data(massart97ex3)
attach(massart97ex3)
xi <- levels(factor(x))
yx <- split(y,factor(x))
ybari <- sapply(yx,mean)
si <- round(sapply(yx,sd),digits=2)
wi <- round(1/(si^2),digits=3)
weights <- wi[factor(x)]
m <- lm(y ~ x,w=weights)
inverse.predict(m,15)
inverse.predict(m,90)