A few days ago, Andrew Gelman responded to a blog article by Ian Ayers, on the found relationship between peoples names and their profession. This relationship (amongst other similar relationship) was fund by Pelham, Mirenberg, and Jones (2002). It was found that many more dentists are called Dennis than would have been expected based on a random distribution of both first names and professions. A mini-theory on Dennis the Dentist is suggested, in which people called Dennis “gravitate toward dentistry“.

But, it this actually so special at all? Or rather: does this mini-theory hold? Gelman nicely shows that using propoer conditional probabilities, the ‘many’ dentists named Dennis, actually aren’t that numerous. Have a look for yourself on his blog: his argument is actually quite simple and elegant.

There is, I think, another reason why the mini-theory on Dennis the Dentist does not hold, and it has all to do with a man called Joe the Plumber.

A rudimentary understanding of causality tells that one can infer causality if three conditions are satisfied: 1) A relationship does indeed exist, 2) The supposed cause comes before the supposed effects, and 3) The relationship is not spurious, in the sense that something else causes both ‘variables’ between which the relationship seems to exist.

Indeed, it is argued, the temporal order seems correct. According to the mini-theory on Dennis the Dentist, people have a tendency to choose a profession that fitst their name. If I understand his blog correctly, Gelman questions the actual existence (or rather: importance) of the actual relationship. Is it actually so unlikely that a few (222 to be precise) more dentists are called Dennis, compared to the fully random distribution of names over professions? Can this not likely be explained by simple random fluctuations?

There is, I would like to add, another reason not to trust the mini-theory on Dennis the Dentist. This relates to the spuriousness of the relationship. What about the name of the father, and what about his profession? Things are rarely uncorrelated in social life, and so it is with the profession of parents, and both the names and professions of their offspring. Parents with high status professions still manage to have their children achieve relatively high status professions as well (on average, that is). But perhaps more interestingly: the names people give to their children are also bound to their social status. For those unfamiliar with this phenomenon, Steven Levitt wrote a lovely chapter about this in Freakonomics.

So, I would like to argue, it might very well be possible that Dennis did not choose his profession to be Dentist because of given name, but has been ‘predestined’ to do so because of the preferences of his parents. And their preferences of course relate to the name they gave to Dennis, as well as the opportunities they offered him to strive for certain types of professions. In other words: I think the Dennis the Dentist correlation is spurious (if it exists at all).

On a final note, this also brings to mind the fact that, although latently, most people are quite familiar with such social phenomena as name-giving and social class. During the presidential elections, John McCain tried to address many people quite a bit lower on the social ladder compared with Dennis the Dentist. So, he sought Joe the Plumber, a move that got him quite a bit of attention. It all fitted: the hard-working, self-made man, who rose a few steps on the social ladder with his own plumbing company. This image strongly appealed to exaclty the people McCain tried to address.

But, think about this: would Dennis the Plumber have been such a strong archetype as well?

Pelham, B., Mirenberg, M., & Jones, J. (2002). Why Susie sells seashells by the seashore: Implicit egotism and major life decisions. Journal of Personality and Social Psychology, 82 (4), 469-487 DOI: 10.1037//0022-3514.82.4.469