In many cases, the frequency of a name does not stay constant over time. Rather, a name goes in and out of fashion in a pattern characterized by its “discovery” by higher socioeconomic classes, followed by subsequent adoption by the rest of the population to benefit from the implication of a higher status. This mass adoption leads to a rise in absolute frequency, which in turn lowers the name’s attractiveness first for the trendsetters who made it popular to begin with, then for the parents who followed – the name begins to lose momentum; some saturate quickly and sometimes nearly disappear for years.

The downside of picking a name which undergoes significant cyclical variation in frequency is that it may “date” your child – most will guess, for example, that Henrietta and Archibald, Augusta and Hector, and Myrtle and Roderick are well into retirement.

One dimension of cyclicality is amplitude. This term refers to the difference between a name’s frequency when it is most popular and when it is least popular. Think of it like this: If there is a period when every other boy is named Jonah, followed by a period where there are no Jonahs, then that name has a high amplitude.

If a name’s amplitude is high, then the name will date your child to the time period in which she was born. People will also perceive her as being “old-fashioned,” for instance, if her name was popular earlier, then stopped being used almost entirely. On the other hand, a name with a low amplitude is timeless. Names like Joseph, Phillip, Paul, and Thomas have been used more or less consistently over the years, and probably will be for years to come. They minimize the risk of “dating” your child.

A second dimension of cyclicality is the period. When you look at the period of a name, you are examining where that particular name is in its cycle. How many years are there, on average, between peaks in popularity for the name? More importantly, where is the name, currently, on the popularity curve – is it about to come back into vogue, is it a falling star or is it likely to remain unique for several years?

Names with a long period and low amplitude typically have very steady absolute frequency. This can be considered a form of insurance against sudden changes in uniqueness, such as fads, which are very important to avoid.