Question about curve fitting...

As you appeared to have received no reply ...

1) Use nls() on the original equation

2) Transforming first and using linear fitting is **NOT** the same. The
error structures differ and therefore you get different results. The
greatest effect is on inferences -- i.e confidence intervals for the
parameters: the usual asymptotic intervals would be symmetric based on the
original scale, asymmetric based on the transformed. For reasonably
well-behaved data the point estimates shouldn't be too much different,
however. In any case, the linearization is a good way to find starting
values.

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA

"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box

Question about curve fitting...

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