sentence1: a complete case analysis would be unbiased , albeit inefficient , if the missingness is conditionally independent of the outcomes given the covariates in the model , even when the covariates have missing data , as is the case here .
sentence2: this approach is valid , even if inefficient , where the probability of missingness is independent of the outcome of interest given the covariates in the analysis model , that is there is covariate-dependent missingness .