First born children in Norway get better education and as adults are more successful in the job market than younger siblings, a Norwegian-U.S. study showed.

“It is the birth order and not necessarily the size of the family that is important,” said economics professor Kjell Salvanes of the Norwegian School of Economics and Business Administration. “It is better if you are the first born.” Salvanes and two colleagues from the University of California, Los Angeles (UCLA) based their study on census data of Norwegians born between 1912 and 1975.

The findings will be published in the Quarterly Journal of Economics, a Harvard publication, in May.

They found that younger siblings tend to get less schooling than their elders and then end up with lower pay on average and were more likely to be in part-time work, Salvanes said. The findings were likely to hold true in other countries, he said.

“In terms of educational attainment, if you are the fourth born instead of the first, you get almost one year less education, and that is quite a lot,” Salvanes told AMN Health.

And first-born children tend to weigh more at birth than their younger brothers and sisters, which is a good predictor for educational success, Salvanes said.

Children alone with two adults also tend to get more intellectual stimulation than children in large families who get less parental attention, he said.

First-born children seem to learn from teaching their younger siblings, contrary to the common notion that younger children benefit by learning from their elders, Salvanes said.

So does that mean big sisters really are smarter?

“Yes. It’s hard to admit because I have older sisters,” Salvanes said.