is it necessary to exclude two discrete factors which variable is true in a linear model can two discrete factors be included if two variables are combined in a linear model what is the outcome when two different variables are exclusions in a linear model, how to model? if two factors are excluded in a linear model which factor can always happen in a linear model? how many combinations of a factor are in a linear model why are two discrete factors used together in a linear model? what can one factor never happen which two factors in a linear model must never happen? how to model a linear model can two factor be true if there is one that can never happen why not include two factors in the linear model. how to exclude two combinations of factors in a linear model why is a discrete model used? what's the difference between an exclusion factor, a discrete factor and a linear model which factor can ever happen in a linear model why two factors need to be excluded in a linear model can two discrete factors be used together to form the outcome