what is the endogenous variable? what is x_tj in r models what is instrumental variable how to use r variable z to model growth trajectories which variable is an endogenous variable which variable is an endogeneous variable in a multilevel mixed model which variable is an instrumental variable what is the instrument variable of a mixed multilevel model which variables can be used in a growth model what is the relationship between an instrumental variable and an endogenous variable? what is the instrument variable on the growth function of the r curve? is j-beta an instrumental variable is the growth trajectories a convariate what is the lag in the endogenous variable which r variable is a linear growth function and which is an endogenous variable what is the difference between an instrumental variable and a multilevel model? a__________. what is the relationship between an instrumental variable and a multilevel model? what is the difference between an instrumental variable and an endogenous variable in r which variable does the model use as an instrument r how to model trajectories of individual