New York:  Interest in “sex” or other sexual terms in online searches rises significantly during Christmas festivities, with more births nine months later, an interesting study has revealed.

It’s often wryly observed that birth rates peak in September, with many studies citing seasonal changes in human biology to explain this post-holiday “baby boom.”

But new research from scientists at Indiana University (IU) and the Instituto Gulbenkian de Ciencia in Portugal has found that spikes in pregnancies are actually rooted in society, not biology.

The study, which appears in the journal Scientific Reports, drew upon data from nearly 130 countries that included sex-related Google search terms from 2004 to 2014 and 10 per cent of public Twitter posts from late 2010 to early 2014.

The analysis revealed that interest in sex peaks significantly during major celebrations — based upon a greater use of the word “sex” or other sexual terms in web searches.

These peaks broadly corresponded to an increase in births nine months later in countries with available birth-rate data, the team revealed.

“The rise of the web and social media provides the unprecedented power to analyse changes in people’s collective mood and behaviour on a massive scale,” said Luis M. Rocha, a professor in the IU School of Informatics, Computing and Engineering.

“This study is the first ‘planetary-level’ look at human reproduction as it relates to people’s moods and interest in sex online,” Rocha added.

To understand the higher interest in sex during holidays, the researchers also conducted a sophisticated review of word choices in Twitter posts — known as a “sentiment analysis” — to reveal that, collectively, people appear to feel happier, safer and calmer during the holidays.

When these collective moods appear on other occasions throughout the year, the analysis also found a corresponding increase in online interest in sex.

“Perhaps people feel a greater motivation to grow their families during holidays when the emphasis is on love and gift-giving to children. The Christmas season is also associated with stories about the baby Jesus and holy family, which may put people in a loving, happy, ‘family mood,’” Rocha mentioned.

According to Rocha, the findings could help public health researchers pinpoint the best dates to launch public awareness campaigns encouraging safe sex in developing countries lacking in reliable birth-rate data.