Here’s the simplest personality test you’ll ever take. It consists of a single, simple question:
Of your siblings, are you the oldest child, second oldest, third oldest etc.?
For over 100 years, psychologists have debated the relationship between birth-order and personality. You’ve probably heard of “middle-child syndrome”; the idea that this child misses out on both the special privileges given to the oldest child, and the allowances made for the baby of the family, and may become withdrawn or resentful as a result. Firstborns are often thought to be care more about pleasing their parents, and to be conscientious and dominant, with laterborns more easy-going, sociable and creative.
However, 2015 saw the publication of two (1,2) very large studies (looking at, together, almost 400,000 people) which showed that these claims are largely myths. Although firstborns did come out as fractionally more conscientious and less sociable than laterborns, they bucked the expected trend by coming out as more agreeable and less neurotic. More importantly, the size of this effect was tiny, with birth order explaining well under 1% (in fact, just a twenty-fifth of 1%) of the variability between different people with regard to personality.
The idea of a link between birth order and intelligence – though less well known – was supported, although again the effect was tiny, with firstborns enjoying a boost of just 1 IQ point (set against an average IQ score of 100).
Overall, the lesson is clear: Whatever your strengths and weaknesses in terms of personality and intelligence, your position relative to your siblings is almost certainly not to blame.