library(foreign)
daisy2<-read.dta("r:/daisy2red.dta")
library(MASS)

# Box-Cox analysis for offset, for simplicity without aut_calv
logtrans(wpc ~ parity+rp*vag_disch+twin+dyst+herd_size+I((herd_size-100)^2), data=daisy2,
         alpha=seq(-0.9, 10, 0.1))
lt <- logtrans(wpc ~ parity+rp*vag_disch+twin+dyst+herd_size+I((herd_size-100)^2), data=daisy2,
         alpha=seq(1, 4, 0.01))
lt
# optimal alpha around 2.75