Rich wrote: << . . . The remark does illustrate the need for at least three data points, for a phenomenon to be called exponential. --- [I wrote:] << A note about "exponential": technically, the term refers to numbers that are increasing by a fixed (compounded) percentage, rather than a fixed amount, per unit of time. So it is entirely possible that the number of schools teaching Chinese has increased by a steady 18% per year from 300 a decade ago to 1,600 today; that would indeed be an exponential increase, though it's unlikely the author of the article did the research to confirm this. . . .

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It may be a bit tricky to know just how many data points are needed, since any finite set of points (t,f(t)) fits some polynomial f(t) = P(t). But I'd also distinguish between technical and common usage of the term. I wouldn't want to encourage common usage of exponential if it merely means "very fast" -- which was the point of the guy who wrote the column at < http://topics.blogs.nytimes.com/2010/02/02/when-spell-check-cant-help-4/ > -- but to use it for something that *isn't* increasing especially fast would be confusing to many (outside of a technical context). --Dan _____________________________________________________________________ "It don't mean a thing if it ain't got that certain je ne sais quoi." --Peter Schickele