Dear list, I have a data set which looks like myDF (see below) and I'd like to estimate the linear model rea=a*rea+b*mod+error, where a+b=1 and a,b>0. I tried mymodel=lm(rea~ st + mod-1, data=myDF) summary(mymodel) but I couldn't get what I'm looking for. Also, I tried RSiteSearch("constrained coefficients in lm") which produces 20 hints, but they're not what I need. Any help would be appreciated. Thanks in advance, Jorge # Data set to estimate the model myDF=read.table(textConnection("rea st mod 14482734 14305907 14761000 14427969 14502228 14848024 14698723 14408264 14259492 15741064 14797138 14565303 15914249 16162714 14348592 16475594 15977623 15592229 17124613 16688456 14988151 17575281 17383822 15647240 17721548 17757635 15624907 18178273 17779858 15598802 18005810 18364233 16363321 18032618 17938963 16536844 17737470 18043063 17096089 17652014 17624039 17056355"),header=TRUE,sep="") closeAllConnections() [[alternative HTML version deleted]]