title: Comments on paper by C. E. Frangakis, D. B. Rubin and X.-H. Zhao.
authors.affiliation: ICRF Cancer Epidemiology Unit, Gibson Building, Radcliffe Infirmary, Oxford OX2 6HE, UK. amy.berrington@cancer.org.uk
authors.forename: A
authors.initials: A
authors.lastname: Berrington
authors.forename: D R
authors.initials: DR
authors.lastname: Cox