The stereotype of the oldest sibling is that of a Type-A overachiever, high-strung and highly successful. The effect of birth order on personality and achievement is something that seems like common knowledge, and there is research to suggest that firstborns have the advantage. But it’s less set in stone than it seems, partly because many studies compared siblings from many families. “Birth order is clearly a within-family phenomenon,” points out a study published by Feifei Bu of the University of Essex as part of the Institute for Social and Economic Research’s Working Paper Series.

Her study takes data on 3,552 people organized into 1,503 clusters of siblings from the British Household Panel Survey (and its successor, the UK Household Longitudinal Study) and looks at how birth order relates to educational aspiration and achievement, both across and within families.

To measure educational aspiration, Bu looked at children’s responses to this question at age 13: “Do you want to leave school when you are 16, or do you plan to go on to sixth form or college?” Future waves of the longitudinal surveys followed up with these children to see the highest level of education they achieved. (Some of the research subjects aren’t yet old enough to have completed college degrees, so she measures instead whether they “gained any qualifications following the end of compulsory schooling.”)