In 1917, the first year for which there are records, King George V sent birthday cards to 24 British centenarians to congratulate them on turning 100. Since the beginning of her reign Elizabeth II has sent over 110,000 100th birthday telegrams/cards to delighted recipients.

In passing, a recent article in The Independent noted the expected number of Britons aged 100 or more would be 100,000 in 25 years time and calculated that our then monarch will be congratulating centenarians “at a rate of 250 a day”.

Two immediate thoughts: a) concern for the future monarch faced with a mountain of cards (all those signatures!) and b) would congratulations really be issued ‘at a rate of 250 per day’?.

Well, no…it’s a lower figure than ONS projects but let’s take 100,000 as the total number of people who are 100 years or more in 2038. This is not the same as the number of people celebrating 100th birthdays in that year. With a life expectancy at age 100 of say 2 or 3 more years, the number passing 100 in 2038, could be estimated at around 30,000.

So already fewer cards in total and ”at a rate of 250 a day” has become”at the rate of 80 a day”. But then, how useful are ’at the rate of’ calculations like this?

Claims in ads and media headlines are often expressed in what are perceived to be more accessible, human-sized, more impactful terms e.g. “one mugging every minute” “one child goes missing every 3 minutes!” or “a tonne of crisps eaten every 3 minutes in the UK”. Sometimes, the total is cited. Sometimes the words ‘on average’ included. Either way, nothing is really happening with the sort of uniform frequency implied and basic averaging like this just disguises the fact that there will be peaks and troughs and clusters of activity. Knowing where the highs, lows and groupings occur is the most useful information.

Revisions of the total and ’average daily rates’ apart, whoever plans the mail-out of 100th birthday cards per year in 2038 will need to know what the seasonal pattern of births 100 years earlier – in 1938 – actually was. In the first half of the 20th century, births in England and Wales showed a large spike in the Spring and a small spike in the Autumn. So it’s likely that the Royal palace will need to ensure a very good stock of cards in April/May and Sept/October.

BTW, the Queen also sends cards to couples celebrating diamond (60th) and platinum (70th) wedding anniversaries. 30,359 diamond congrats were issued by the Palace in 2011. If trends in the UK’s marriage and divorce rates continue, the need for fewer of these anniversary cards may begin to offset some of the burden of increased birthday messages.

Or then again, our sovereign may just review the policy and raise the age threshold that warrants a card.