x = age
y = Relative Spinal bone mineral density

Source:

"bone" data set from http://cran.r-project.org/web/packages/ElemStatLearn/ElemStatLearn.pdf

We obtained and preprocessed the data using the following R commands:

install.packages('ElemStatLearn')
library(ElemStatLearn)
boneuniq = bone[1,]
for( i in 2:dim(bone)[1] ) { 
  if( bone[i,1] != bone[i-1,1] ) { 
    boneuniq <- rbind(boneuniq,bone[i,])
  } 
}
write.table(boneuniq[,c(2,4)],file='/tmp/bone.csv',row.names=FALSE,col.names=FALSE)
remove.packages('ElemStatLearn')

For the preprocessing, we only take the first measurement for each child, and 
selected only the columns "age" and "spnbmd" (Relative Change in Spinal BMD).

The ground truth should be that age causes relative change in spinal BMD.