The other day, having read one book described as “one of the best-selling books of the 20th Century” and another as “one of the best-selling books of all time,” my brain starting spinning in amateur research mode.

My first question was: what does “one of” mean?  Does it mean the 3rd best-selling book of all time? The 22nd?  Among the top 1000?

As one might expect, Wikipedia has a list of the best-selling books of all time, with various estimates of total sales.  But, with books from the 19th and 20th Centuries on the list alongside ancient works, Analytic Me started to wonder about rates of sale.

After all a train that travels 100 miles in 10 hours is nowhere near as fast as a train that travels only 1 mile in 1 minute.  Likewise a book that sells a million copies over a thousand years is not being chosen at the same rate as a book that sells two thousand copies in a single year.

And, to answer the objection that a book like the Bible wasn’t selling at a steady ready over time (particularly before the invention of moveable type), I would point out that it still had centuries during which to drum up support and publicity.

So let’s take a look at how the numbers crunch.

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