PGR and neoplasm: We generated missing data at random (MAR) in five covariates (tumour grade, number of positive lymph nodes, hormonal therapy, chemotherapy, and progesterone receptors) with the probability of missingness depending on age and tumour size (probability of missingness e−9 + 0.1 × age − tumour size 2/(1 + e−9 + 0.1 × age − tumour size 2)).