Growing up in a home packed with books has a large effect on literacy in later life – but a home library needs to contain at least 80 books to be effective, according to new research.

Led by Dr Joanna Sikora of Australian National University, academics analysed data from more than 160,000 adults, from 31 different countries, who took part in the Programme for the International Assessment of Adult Competencies between 2011 and 2015. All participants were asked how many books there were in their homes when they were 16 – they were told that one metre of shelving was equivalent to around 40 books – and went through literacy, numeracy and information communication technology (ICT) tests to gauge their abilities.

While the average number of books in a home library differed from country to country – from 27 in Turkey to 143 in the UK and 218 in Estonia – “the total effects of home library size on literacy are large everywhere”, write Sikora and her colleagues in the paper, titled Scholarly Culture: How Books in Adolescence Enhance Adult Literacy, Numeracy and Technology Skills in 31 Societies. The paper has just been published in the journal Social Science Research.

“Adolescent exposure to books is an integral part of social practices that foster long-term cognitive competencies spanning literacy, numeracy and ICT skills,” they write. “Growing up with home libraries boosts adult skills in these areas beyond the benefits accrued from parental education or own educational or occupational attainment.”

Teenagers in a home with almost no books went on to have below average literacy and numeracy levels, the researchers found. Having approximately 80 books in adolescent home libraries raised levels to the average, while once the library size reached 350 books, it was “not associated with significant literacy gains”. The same was true for ICT skills, but the gain was not as steep.

According to the paper, teenagers with only lower levels of secondary education, but who came from a home filled with books, “become as literate, numerate and technologically apt in adulthood as university graduates who grew up with only a few books”. The university graduates who grew up with hardly any books around them had roughly average literacy levels, said the researchers. So did those whose schooling ended in the equivalent of year nine (13-14 years old), but who grew up surrounded by books. “So, literacy-wise, bookish adolescence makes for a good deal of educational advantage,” the authors claim.

The same was found to be true for numeracy, leading the academics to claim that “adolescent exposure to books compensates for shortcomings not only in adult literacy but also numeracy: its impacts are equivalent to additional years of education.”

Sikora said: “As expected, respondents’ education, occupational status and reading activities at home are strong predictors of superior literacy nearly everywhere, but respondents clearly benefit from adolescent exposure to books above and beyond these effects. Early exposure to books in [the] parental home matters because books are an integral part of routines and practices that enhance lifelong cognitive competencies.”

The paper raised the possibility that the move towards a digital culture could reduce the impact of printed books, but said that “for now … the beneficial effects of home libraries in adolescence are large and hold in many different societies with no sign of diminution over time”.

“Moreover, home library size is positively related to higher levels of digital literacy, so the evidence suggests that for some time to come, engagement with material objects of scholarly culture in parental homes – ie books – will continue to confer significant benefits for adult ICT competencies,” concludes the report. “For the time being … the perception that [the] social practice of print book consumption is passe is premature.”