The first examination that took place was the effect birth order has on intelligence. This study …show more content…
When the effect of birth order on personality was investigated, the researchers found that the birth order position had no effect on four out of the five personality traits these were; extraversion, emotional stability, agreeableness, or conscientiousness in the two groups studied.in another study carried out by Sulloway (1999) it was found that birth order has no effect on emotional stability either. Because of the different volumes of intellect on the openness scales it lead to incoherent results.
Another test between first-borns and later-borns took places reusing the results of the within- and between-families, the results of this study found that first-borns have slightly higher intelligence and intellect, which is much the same as the previous study. Likewise it was found that birth order had no significant effect on personality.
Following a hypothesis of Healey and Ellis (2007) that choosing siblings with an age gap between 1.5-5 years gives a clearer result of birth-order effects, a further study took place where only siblings ranging between this age gaps were participants. Similar to the other experiments the results showed that only intelligence and openness to experience were