Hi again folks,

Another question I have hard time to resolve : How can I force a mixed model to pass through the origin (no intercept) ? Actually, as I'm modelling the basic relationship between age and diameter of a tree species, I want that at age = 0, diameter = 0, (or at log(age) = 1, diameter = 0) whatever the levels of my random variable is (which is the plot). In this case, of course, I cannot specify a random intercept since there is no intercept...

My neophyte guess would be to first specify that I want a random slope for dbh (diameter at breast height) per plot. But where should I specify that I dont want any intercept? Is it feasible (or even scientifically wishable?)?

My model is :

PICE.MAR_tree_age_model_cand[[1]] <- lme(log(age_tree) ~ Temp + Prec + dbh_tree, random=~dbh_tree|plot_name, data = PICE.MAR_tree, control=lmeControl(maxIter=500, niterEM=500), method="ML")

I guess it's more complicated than to add "-1" in the formula above as in lm (well here, since it is log(age_tree), it must go through "(0,1)" and not (0,0)). I'm puzzled...

Thanks,

Yan




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