what is the default covariance structure in glmer and can it be changed? what is the default covariance structure on glimmix what is covariance in glmer what is the default covariance structure in glimmix what is the default covariance structure for glimmix glmer default covariance definition what is the default covariance in glimmix what is the default shape in glim what is the default covariance structure what is glmer default covariance structure what is the default covariance structure in glimmix what is the default covariance structure what is glmer used for what is covariance structure in r default covariance structure glmer what is glimmix covariance what is glmer's default structure what is covariance what is glmer? what is the name glmer function