Model functions

mu

mu is used to fit the intercept/constant term. It is normally present and listed first in the model. It should be present in the model if there are no other fixed factors or if all fixed terms are covariates or contrasts except in the special case of regression through the origin.

Trait

Trait is used with multivariate data to fit the individual trait means. It is formally equivalent to mu but Trait is a more natural label for use with multivariate data. It is interacted with other factors to estimate their effects for all traits.

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