Fabien Lebugle wrote: > I am a master student. I am currently doing an internship. I would > like to get some advices about the following issue: I have 2 data > sets, both containing the same variables, but the data were measured > using two different procedures. I want to know if the two procedures > are equivalent. Up to know, I have built one linear model for each > dataset. The two models have the same form. I would like to compare > these two models: are they identical? Are they different? By how > much? > > Please, could you tell me which R procedure I should use? I have been > searching the list archive, but without success...
This is not a question of ``which R procedure'' but rather a question of understanding a bit about statistics and linear models. You say you are a ``master's student''; I hope you are not a master's student in *statistics*, given that you lack this (very) basic knowledge! If you are a student in some other discipline, I guess you may be forgiven. The ``R procedure'' that you need to use is just lm()! Briefly, what you need to do is combine your two data sets into a *single* data set (using rbind should work), add in a grouping variable (a factor with two levels, one for each measure procedure) e.g. my.data$gp <- factor(rep(c(1,2),c(n1,n2))) where n1 and n2 are the sample sizes for procedure 1 and procedure 2 respectively. Then fit linear models with formulae involving the grouping factor (``gp'') as well as the other predictors, and test for the ``significance'' of the terms in the model that contain ``gp''. You might start with fit <- lm(y~.*gp,data=my.data) anova(fit) where ``y'' is (of course) your reponse. You ought to study up on the underlying ideas of inference for linear models, and the nature of ``factors''. John Fox's book ``Applied Regression Analysis, Linear Models, and Related Methods'' might be a reasonable place to start. Bon chance. cheers, Rolf Turner [EMAIL PROTECTED] ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.