Sheffe models

The two common types of model, one widi an intercept and one without an intercept term, are related. Models excluding the intercept are often referred to as Sheffe models and those with die intercept as Cox models. Normally a full Sheffe model includes all higher order interaction terms, and for diis design is given by... 

The design matrix is given in Table 2.35, and being a square matrix, the terms can easily be determined using die inverse. For interested readers, the relationship between die two types of models is explored in more detail in die Problems, but in most cases we recommend using a Sheffe model. 

Each type of blend yields an equivalent number of interaction terms in the Sheffe model. Hence for a live component mixture and three component blends, there will be 5 /[(5 — 3) 3 ] = 10 mixtures such as (1/3 1/3 1/3 0 0) containing all possible combinations,... 

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