what is mz twins what is the covariate for concordant twins what is the categorical variable of a twin? how do i fit a mixed effect model which covariate are used for a mixed effect model how do you model the mz twins mixed effect model for mz twins which mz model use dummy covariates what type of variable does mz twins have what is the dummy variable in a mixed effect regression why use mixed effect model for mz twins in regression what is a concordant pair how to correctly fit a mixed effect model what is the mix of effect variables for mz twins what is the model of concordant twins why mz twins need mixed effects how do i find out the concordant twin status which of the following is a categorical variable? what is the mixed-effects model for mz twins how to use mixed effects model