On Thu, 14 Sep 2017 21:28:31 +0100, "NY" wrote:

snip

I'd say the best approach would be to find a transformation (eg y=log(x) or
y=sqrt(x)) which gives a good, well-correlated straight line. Then
extrapolate that and do an inverse transformation (eg antilog or x-squared)
on the predicted value. Obviously the more data points you have, the better
prediction you can make and the better you can construct a least-squares
regression line for extrapolation and then back-transformation.

Yeah, I was going to say that but thought it was obvious. ;-)

Cheers, T i m