What's in a name?

Lets think about my name. Even though Stephen is fairly common first name, you hear the last name Flood much less frequently.

To simplify things a bit, lets assume (pretend) that first and last names are independent. Then \[P(\text{Full name}) \approx P(\text{First name})*P(\text{Last name})\] and \[\text{Occurances of your full name} = P(\text{Full name})*\text{Total population}\]

Now we need to find out the rate at which each name occurs.

• According to this site, the 2000 US census found that "out of 100,000 people in the United States, [the surname] FLOOD would occur an average of 6.17 times." In other words \[P(\text{Flood}) = \dfrac{6.17}{100,000} = 0.0000617\ ( = 0.00617\%) \]
• According to this site " there were 842,384 people named Stephen out of the 335,174,936 people born between 1914-2013, giving \[P(\text{Stephen}) = \dfrac{842,384}{335,174,936} = .0025\ (= .25\%)\]
• Putting this together, we get \[P(\text{Stephen Flood}) \approx 0.0000617 * .0025 = 0.00000015425\ (= 0.000015425\%) \]

This sounds pretty uncommon. But the US population is fairly large. According to census.gov, the current US population is a bit below 319,000,000 people. \[\text{Occurances of Stephen Flood in the US} \approx 0.00000015425*319,000,000 = 49.2 \] So we might expect to see about 49 Stephen Floods in the US. We would expect to see more in the world at large, but we'd need to recalculate the relative frequency to know how many more people to expect.

In fact, whitepages.com records around 100 people with the name "Stephen Flood" in the US and Canada, and there are probably many more.

And indeed, a quick web search reveals a number of different 'Stephen Flood's in the US

• A photographer for the Lehigh Valley newspaper the Express Times
• A Doctor of Family Medicine in Massachusets
• An Orthopedic Surgeon in Louisiana

Looking outside the US, we even find a couple of academics named "Stephen Flood"

• A Postdoctoral Research Fellow at the Climate Change Research Institute (CCRI) in Victoria University of Wellington, New Zealand
• A Research Student in Physics at Lancaster University in the UK