The Fastest Growing Blog In The Universe

Is probably one which was started only a few hours ago. It will get several readers in the first day (at least the blogger will visit to admire her or his handiwork and some friends might, too). When the visitor meter goes from one to two visits, the percentage increase is 100%!

Why am I writing about something so silly? Because a very common misreading of the idea of "fastest growing" (religion, firm, idea) tends to ignore the simple fact that percentage increases are always enormous at first if we start from somewhere close to zero and if what we count is measured in discrete units, such as in my example of blog readership. To add 100 visitors per day to a blog which gets 500 initially means a 20% increase. To add 1,000 visitors to a blog which gets 100,000 visitors a day is an increase of 1%. But the latter is more people...

I've seen the "fastest growing" idea used to explain why certain rare diseases will soon swamp our whole health care system - because they are growing so rapidly - when that is just not true. I've also seen the same argument being used for all sorts of fairly rare religions in the U.S., with the implication that soon these religions (such as Wicca) will take over Christianity as the dominant denomination.

It's irritating. And it's based on a misunderstanding of how percentages behave. Always look at the base, my little grasshopper, as my grandmother used to say, before you get all excited about some growth rate. Or as my grandmother would have said had she thought about it.
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For those having deja vu all over again, yes I wrote on this topic a couple of years ago. But nobody listened...