Bioequivalence and Bioavailability Forum

Dear Elmaestro,

Firstly, if you look at this previous post and compare with what I got here (part of type I SS), you will find out that R does different calculations with the model of (Cmax ~ seq + prd + drug + subj) and the one (Cmax ~ prd + drug + subj + seq) for type I SS. Apparently, the list "sequence" of fixed variables can result in differences for type I SS. The seq was disappeared! Amazing thing, another finding in lm() of R. Secondly, due to the different type I SS calculation, the anova() function had different "sequence" list of these fixed variables. That's why I took a lot of time to locate "subj(seq)". That's weird. I checked with R on-line help (chm), and it said that "quoted...The models fit by, e.g., the lm and glm functions are specified in a compact symbolic form. The ~ operator is basic in the formation of such models. An expression of the form y ~ model is interpreted as a specification that the response y is modelled by a linear predictor specified symbolically by model. Such a model consists of a series of terms separated by + operators. The terms themselves consist of variable and factor names separated by : operators. Such a term is interpreted as the interaction of all the variables and factors appearing in the term..." in "formula". And also "quote...Models for lm are specified symbolically. A typical model has the form response ~ terms where response is the (numeric) response vector and terms is a series of terms which specifies a linear predictor for response. A terms specification of the form first + second indicates all the terms in first together with all the terms in second with duplicates removed. A specification of the form first:second indicates the set of terms obtained by taking the interactions of all terms in first with all terms in second..." in the section of Details of lm(stats). In the model that you proposed, it was written as (Cmax ~ prd + drug + subj + seq). R automatically drops the variable (or factor) seq out of its included with this model in calculation type I SS, but not with the previous of (Cmax ~ seq + prd + drug + subj) or others. I'm playing with lm() right now with different list sequences of fixed variables to see what I can get. Interesting, uh?

❝ I am sure you are not. But I lost it slightly here, could you explain me

❝ what your concern is?