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A new study shows that for men, access to books from a young age corresponds to higher earnings over a lifetime.

Economists from Italy’s University of Padova compared data on 5,820 European men to see if longer compulsory childhood education could increase kids’ earnings over a lifetime. It does: Averaged across nine countries, boys who attended an extra year of school due to changing age requirements eventually returned an additional 9% of income.

But the researchers were surprised to find that, among kids who benefited from an extra year of school, those who grew up with more than 10 non-school books (that is, books they weren’t forced to read) at home eventually doubled that lifetime earning advantage, to 21%. Factors like whether the boys’ fathers had white-collar jobs, and whether their homes had running water, did not seem to make a difference.

Crucially, there was no significant difference between whether participants reported having 50, 100, or 200 books growing up. The key was whether they grew up with any number of books greater than 10.

The researchers based their models on data collected from men between ages 60 and 96 from Austria, Belgium, the Czech Republic, Denmark, France, Germany, Italy, the Netherlands, and Sweden, part of a massive ongoing survey of Europeans. They compared whether the men grew up in rural or urban environments, the years they were in school, roughly how many books they had in their houses at age 10, and their income across their lives. The study was published online in April in The Economic Journal.

Of course, this doesn’t show causation between books and salaries. As researcher Guglielmo Weber says, “Children who grew up in homes with books may have more chances to learn about life and the universe, and to have new experiences through books. Or it could be because homes with books capture families with stronger cultural and socioeconomic backgrounds.” In other words, books themselves could spark curiosity and ambition, but they’re also a sign of a house that encourages knowledge-seeking, or has a higher income from the start.

The survey focuses on men born long before the internet could bring information at lightning speed to any kid with fingers and eyeballs, but Weber believes that books remain a significant indicator of future financial success today. “Even nowadays, books capture something,” he says.

Image by Alba Sanchez Peral from Flickr, licensed under CC BY-SA 2.0.