random effects model does random effect mean what makes a degenerate model which linear model is not degenerate? __________ is considered a random effect when a variance is zero what is the difference in an estimation of variance and standard deviation can you include time with an sd in a mixed effect? a variance of zero does not mean that there is no variability between the groups. why does random effects include time is time of data considered random if random variable is zero in a mixed-effects model, does this mean why sd is zero variance why does random effect occur why is time a random effect in a mixed effect model is random effect linear what is the random effect in mixed-effects models is it reasonable to include random effects in a simulation why is it ok to have random effects which model is degenerate is time a random effect model