This thesis includes three empirical studies, analyzing how sibling configuration (i.e. birth order, birth spacing and sex-composition) influences siblings’ long-run income and educational choice. This is done by utilizing the unique linkage opportunities of administrative registers covering the entire population of Sweden.

Study I: This paper focuses on how different birth spacing intervals are associated with income rank from ages 33 to 42 years, for siblings in two-child families. The results show clear differences between first- and second-born siblings. At the more common spacing intervals (less than 5 years), spacing has a negligible association to second-born children’s long-term income rank. However, first-born children have lower income rank when a younger sibling is born when they are very young. Having relatively high spacing intervals (over 5 years) is associated with somewhat lower long-term income-rank than having mid-length intervals for both first- and second-born siblings.

Study II: This study focuses on the association between combinations of sibling configuration (i.e. birth order, birth spacing and sex composition) and long-run income rank of siblings. The results show that the significance of different family factors in two-child families vary by sibling sex-composition. The findings suggest that both birth order and birth spacing are important factors for first born boys independent of the younger sibling’s sex. First-born girls, however, only have an advantage if they have a younger sister. More surprisingly is that this advantage does not seem to vary by birth spacing.

Study III: This study examines how sibling gender configuration in Swedish two-child families influences the choice of so-called STEM educational fields (i.e. Science, Technology, Engineering and Mathematics). The results show that younger siblings, net of parental characteristics, are more likely to choose a STEM field if their older sibling already has attended a STEM program. The findings indicate that boys’ choice of STEM fields is independent of having an older brother or sister who has attended a STEM program. However, girls seem to be more likely to choose a STEM-field if they have a sister who has attended a STEM program, than if they have a brother with a similar program. Given that STEM-fields are markedly male dominated, this indicate the importance of having a same-sex role model for making gender atypical educational choices.