How do you measure a trend? To these researchers, it seems to be about numbers at peak popularity, and perhaps about staying power. I would measure a trend by how rapidly it spread, and how rapidly it faded away. For names, that means that there are some people whose age you can guess fairly accurately simply by knowing their first name. Kohl/Cole might be such a name for boys. There are three in my son’s age group basketball league at the Y; I don’t know anyone else with that name.
Does it always make sense to measure trends the same way, or how should trends other than names be measured?