Table 1.

Models exploring the association between age at menarche and sibling relatedness. Model 1 presents the univariate model between age at menarche and sibling relatedness. Model 2 presents a univariate analysis of father absence and age at menarche. Model 3 combines sibling relatedness and father absence in the same model. Model 4 includes all potentially confounding variables. Model 5 presents an optimized version of the full model, retaining only variables associated with age at menarche (p < 0.1). For parameter estimates for the additional confounding variables in Models 4 and 5, see electronic supplementary material, table S4. 95% CI are displayed in brackets. P-value codes: <0.1; **<0.05; ***<0.01; #<0.001.

variableModel 1 (n = 2922)Model 2 (n = 3743)Model 3 (n = 2921)Model 4 (n = 2297)Model 5 (n = 2545)
sibling relationship (ref: only full siblings)
 only half/step-siblings−0.42 [−0.18; −0.67]***−0.37 [−0.11; −0.63]**−0.38 [−0.1; −0.66]**−0.4 [−0.15; −0.65]**
 no siblings−0.15 [0.02; −0.32]−0.13 [0.04; −0.3]−0.2 [0.01; −0.41]−0.23 [−0.05; −0.4]*
 half/step- and full siblings−0.13 [0.05; −0.31]−0.09 [0.1; −0.29]0.06 [0.29; −0.18]−0.04 [0.15; −0.23]
father absence (ref: no father absence)−0.23 [−0.12; −0.33]***−0.11 [0.06; −0.27]−0.14 [0.05; −0.33]
additional confounding variablesnononoyesayesb
  • aAdditional confounding variables in model: birthweight, mother's highest education level, presence of severe financial problems, home ownership status, mother's age at menarche and total number of siblings.

  • bAdditional confounding variables in model: mother's highest education level and mother's age at menarche.