Why is the letter J so common in names of people who go by their initials?

I've met a number of people who use their initials as a name. Almost all of the ones I've met have a "J" as one of the initials. I've asked a few friends, and so far, anecdotally, it seems that this observation holds true.

"J" is of course a common initial, but not common enough, I think, to explain this.

My question is in two parts: Does the observation hold true for you? That is, of the people you know who use their initials as their name, do the overwhelming majority have a "J" as one of the initials? And: can you explain why this might be?

Answer

The reason may be that J. usually stands for John.

In many (if not all) European countries, there is a tradition of using double first names, as in "John-Peter", "Jean-Marc", "Franz-Johann", "Jan Pieter", etc. Notice that hyphenation is immaterial. Variations of John are most probably the commonest element in male double first names; I know for a fact that they are in Dutch, and what evidence I have seems to point to this being the case in other languages too. Since double first names are the kind of first names that are most commonly initialized, being longer than simple first names, it follows that they will contain a disproportionate number of J's.

It makes sense when you think about it: the better known a word is, the more chance that it will be abbreviated. You would sooner abbreviate Mister as Mr than archaeopalaeontologist as ap. The Romans, for example, had a very limited number of first names:

In the early centuries of the Roman Republic, about three dozen praenomina seem to have been in general use at Rome, of which about half were common. This number gradually dwindled to about eighteen praenomina by the 1st century B.C., of which perhaps a dozen were common. — Wikipedia.

That is why it was possible to use one or two-letter abbreviations for most names without ambiguity. So Marcus was M., Publius P., Cnaeus Cn., etc.