why is variability of quadratic slope fixed why is quadratic slope variable fixed what is the variance of the quadratic slope in a growth mixture model what variable can be used to predict the variance in a growth mixture model? how do you use the variance of quadrants in regression what is the variance of the quadratic slope in a growth mixture model? what is the variance of the quadratic slope in growth mixture why is the variance of a quadratic regression parameter fixed at zero why is a variance parameter used in regression analysis what is the variance variable in a growth mixture model why is variance fixed at zero in growth mixture model which parameter cannot be used for the structural part of the model? why are variance of variables in a growth mixture model fixed which parameter cannot be used in regression why is variance a parameter in growth mixture model why cannot a model be used for structural variables why variance of quadratic slope is fixed at zero for growth mixture why does it not use structural parameters to measure variance can a variance be used for a model with fixed effects why is variance fixed at zero in growth mixture models