why should i include variables in my model why are variables included in a linear model a study that is designed to compare groups can be conducted by adding variables. why should the stdev be included in a gl model if a group is matched on which variable in the model, can the group a be excluded? which variable is included in a group comparison what variables match in a group when compared to groups on variables why should i include x in the group compare model is x a variables in a group is x included in the group comparison is group a covariate why is x included in the gls model can you use group vs group c to compare results is it necessary to include x in a group comparison what is the effect of x in the model? why do you have to include the variables for a group in a regression model if I include variable X in a group comparison model, what happens to normal distribution of means? when do you have to include a variable in a general linear model why do I need to include group a and b on x