1. Ease of conception in mothers of twins;Allen, G.; Schacter, J.;Social Biology,1971
2. The effect of parental age, parity and duration of marriage on the twinning rate;Bulmer, M.G.;Annals of Human Genetics,1959
3. On the size of families containing twins;Edwards, A.W.F.;Annals of Human Genetics,1960
4. Twinning in relation to the marital status of the mother;Eriksson, A.W.; Fellman, J.;Acta Genetica et Statistica Medica,1967
5. Influence of combinations of sexes of children on family size;Gray, E.; Morrison, N.M.,1974