Personality and birth order in large families

The influence of birth order on the personality traits of siblings belonging to large families (⩾6 siblings) was investigated using 361 sibling members (190 females, 171 males, mean age 32 ± 9.14) belonging to 42 large families. The personality traits of Psychoticism, Extraversion and Neuroticism were quantified for each participant who completed the Eysenck Personality Questionnaire. Overall, the youngest and three youngest siblings significantly differed from the oldest and oldest three siblings for Extraversion within and across families. The effects of age, gender and family size category on these personality traits were examined based on a hierarchical linear model. An age effect was detected for Extraversion in the model, whereas gender and family size did not have an impact. The age effect held for the two sensitivity analyses and is suggestive of a birth order effect.