One of my acquaintances, who also happens to be a statistics professor, was shocked to see that 34 of his nearly 3,000 Facebook friends – or a startling 1 out of 87 – were born on January 1. He wondered, “Probability theory fails!” But is it actually the case? Maybe not.

Perhaps because it’s the default birth date for those who are unsure or choose not to disclose the precise day. Actually, I also looked through my friend list on Facebook. The number of January 1 birthdays is also disproportionately high there. I’m quite sure that this might happen to many readers as well. Many people should have birthdays on January 1, the first day of the year in the Gregorian calendar.

Satyendra Nath Bose, Vidya Balan, Asrani, Nana Patekar and Jyotidatya Scindia are among the Indian celebrities – past and present – who could celebrate their birthdays and the New Year together. Apparently, there’s nothing special about a January 1 birthday, though. If we assume that births occur at a constant rate throughout the year, which the abovementioned acquaintance of mine assumed, perhaps, then one in every 365 (or one in 365.25, to be more precise) people should be born on January 1.

That represents almost 0.27 per cent of the population. January 1 is only a point in the infinite hoop rolling of time as the earth revolves around the sun and on its axis; it cannot be the start or the finish of the earth’s one elliptical revolution. However, January 1 is significant because it was the first day of the year when Julius Caesar changed the calendar, in part to celebrate Janus, the Roman god of beginnings, whose two faces gave him the ability to see both the past and the future.

However, as Pope Gregory modified the Julian calendar and established January 1 as the first day of a new year, it gradually gained acceptance throughout Europe and beyond. There are many other platforms where users can designate January 1 as their “default” birthday. Because of such “default” logic, there are some villages in India where, as per Aadhaar data, all the inhabitants were born on January 1. According to a media report, Kakra village in Shivpuri district of Madhya Pradesh is one where the majority of villagers lack any documentation proving their age. Therefore, the authorities in charge of enrolling Aadhaar applicants provided them with the identical birth month and date. Likewise, January 1 is the birthday of the majority of people who live in Kanjasa village in the Jasra block of Gurpur, Allahabad. Reports state that almost every resident of Gaindi Khata village of Van Gujjars in Haridwar had the same birthdate on their Aadhaar cards.

In a press release, the UIDAI stated that as per its enrolment policy, where a person doesn’t know the exact date of birth and doesn’t have a supporting document for the same, the UIDAI accepts the declared birth year or age, and January 1 of that year is considered the person’s date of birth for the purpose of Aadhaar enrollment. But this is not exclusive to India. The birthday of thousands of immigrants and refugees around the world is New Year’s Day.

January 1 is picked by default since many of them don’t have access to their birth certificates and because some of them fled some sort of calamity in a region of the world where birthdays aren’t as significant. A few years ago, a Business Insider piece referred to US immigration data from 2009, indicating that 11,000 out of the almost 80,000 refugees who entered the country that year had January 1 as their birthdate.

Even if you don’t assume a uniform distribution of births throughout the year, that still represents an improbably high 14 per cent. Since they lack official birth certificates, these migrants are frequently instructed to put down January 1 as their date of birth when they arrive in the US seeking asylum. The January 1 birthday is so popular among newcomers that, at the stroke of midnight, immigrant children wish their parents a Happy Birthday in addition to wishing them a Happy New Year! Australia, too, experiences the same thing. In the past, people in Australia who lacked proof of their date of birth were assigned a date, with many being forced to use the first day of the year.

Following a change in regulation in 2011, December 31 was designated as the official birthday of individuals in Australia. Australians of the Stolen Generation rarely possessed official documentation, but when they did, their birthdate was July 1 instead of January 1. However, in general, one might wonder if a January 1 birthday is just as likely to occur on other dates. Clearly, the answer is “no” in many societies. In fact, they are far less likely, for reasons some of which are well understood.

In fact, New Year’s Day is really one of the least popular birthdays for native-born Americans, despite the fact that January 1 is an incredibly common birthday for immigrants. After analysing birth data from 1994 to 2014 in the US, the esteemed polling organisation FiveThirtyEight placed January 1 as the 365th day out of 366, surpassing only Christmas Day. They cited a variety of factors to account for the popularity or unpopularity of specific dates, such as parents going into labour early to avoid hospital holidays, Leap Day, or even Friday the 13th. Similarly, in some other countries, like Australia, January 1 may rank among the least popular days to be born.

First of all, hardly any people appear to find giving birth a pleasant way to spend a vacation. It’s likely that doctors would also rather unwind during the holidays than do baby deliveries. Christmas Day, Boxing Day (December 26), New Year’s Day, Australia Day (January 26), and Anzac Day (April 25) are the five least popular dates for births in Australia, for example.

Nonetheless, there may be several ways in which society reflects the custom of using January 1 as the “default” or cut-off date for a variety of activities. Malcolm Gladwell, for instance, noted in his 2008 book “Outliers: The Story of Success” that a disproportionate number of professional hockey players in Canada are born in the early months of the year. The rationale for this is that because youth hockey leagues base their eligibility on the calendar year, they designate January 1 as the cut-off.

As a result, kids born on January 1 participate in the same league as kids born on December 31 of the same calendar year. And at that early age, children born in January or February, for example, are considered better athletes and are obviously more physically mature than their younger counterparts, who are born in the later part of the year.

As a result, they receive extra coaching and have a higher likelihood of being selected for elite hockey leagues. This kind of situation holds true in many other countries and circumstances. Therefore, the “default” cut-off date, whatever that is, might have a significant imprint on society. Regardless, I wish every reader a Happy New Year. And to everyone having a January 1st birthday, Happy Birthday too!

(The writer is Professor of Statistics, Indian Statistical Institute, Kolkata.)