Abstract
Introduction. Birth order was shown to affect various psychological characteristics, ranging from personality to sexual behaviour.
Several previous studies also suggested firstborn advantage in educational achievements. However, others did not find such effect.
This might be due to neglecting possibly modulating factors such as gender and age-gap among siblings. Thus, while taking into account these modulating factors, in our study we focused on the effect of birth order on educational achievements.
Methods. We collected birth order data (including gender and age-gap of respondents and their siblings) from two cohorts of Charles University biology students (cohort 1: students from 1990-1995, N=271; cohort 2: students from 2011-2015, N=1355).
Proportions of firstborns in both cohorts were compared with population data obtained from the Czech Statistical Office. The gender, age gap between siblings and family size were controlled.
Results. In both cohorts, we found significantly higher proportions of firstborns when compared to the population.
We also observed a decrease in representation of firstborns in the second cohort set. Further, closer age-gap between siblings increased the proportion of firstborns, although there are some gender differences.
This effect is stronger among women. Conclusion.
Our results support previous findings on the firstborn advantage in educational achievements. They also highlight the importance to control for gender and age-gap among siblings.
We suggest replication of our results and further testing of the age-gap effects for example in personal traits data.