Material related to Biometrika 2024 article on the conditional logistic regression fitted by Lionel Penrose and Ronald Fisher in 1934. 1934 Articles The relative aetiological importance of birth order and maternal age in mongolism.       Penrose LS. Proceedings of the Royal Society B 115 431-450. A method of separating the relative aetological effects of birth order and maternal age, with specific reference to mongolian imbecility.       Penrose LS. Annals of Eugenics 6 108-132. Data set Penrose's 1934 Data: 217 sibships with at least one child with DS (.csv)       The dataset was reconstructed from the appendices to the two 1934 articles.       It has information on 224 affected children (the no. reported in the articles),       but on 806 unaffected children (rather than the 807 reported) Archives Birth Order and Down's syndrome Correspondence at Wellcome Library Penrose Papers at UCL Digital Collections R A Fisher Correspondence Files at University of Adelaide James.Hanley@McGill.ca October 16, 2024.