(Submitted by reader Robert Wilson)

I joined the Royal Australian Air force in 1972. During the ’70s recruitment was high, so it was not uncommon to have  flights of 20(ish) trainees graduating each week or so. On my first pay parade (we all got paid in cash after a lengthy line up) we all stood at-ease awaiting our name to be called out.

When the paymaster shouted out our names, family name first, first name last, we would then snap to attention and march forward for our pay.

This is how it went:

“Wilson, Robert”…. two of us stepped forward!

No problem thinks the paymaster as he glances down at the pay slip and announces, “Wilson, Robert, William”

The both of us stood firm!

He then read out the 6 digit ID number, and we were separated by less than 100 numbers if memory serves (numbers are issued sequentially which just means we joined about the same time).

So, what are the odd of having identical names, and joining the air force within weeks of each other?

Below are the extended notes provided by Barbara Drescher for use in Skepticality Episode 200. Take a look and leave your comments below.

It’s not easy for me to put numbers on the probability of this happening because name frequencies in Australia were hard to find. However, I did find that the names “Robert” and “William” were as popular there in the 1960s (I assume that the author was between 17 and 25 when he joined) as the were in the U.S., where they took the 5th and 7th spots, respectively. As we’ve seen in past episodes, “Robert” is an enduring name; it was the #1 name for baby boys for decades and has not left the top 100 in more than a century. In the 1960s, “Robert” was the first name in 14,000 boys for every million born and “William” in every 10,000. There is no readily-available source to determine the probability that “William” would be chosen for a middle name, so the first name frequency will have to serve.

The surname name of “Wilson” is also a very common one, but it is difficult to determine just how common it was in Australia at that time. Today, “Wilson” is ranked 5th, occurring in 5,037.98 of every million people. This has probably changed a bit since the 1960s, but it’s our best estimate.

So, 140 of every million boys with the first name of “Robert” will have the last name of “Wilson”, and 1.4 of those will have the middle name “William”. This means that, for every 10 million men this author will meet around his age, 15 will probably share his full name.

The probability of joining the Air Force so close together adds a degree of complexity and to do it justice would require more accurate information about the distributions of these names across ethnic groups and as well as the distribution of ethnic groups in the military. Without that information, my best guess is the probability that another man in a selection of 100 will have this name, given that the author does, which is about 1 in a million.