# Re: st: RE: S-Curve/logistic curve regression

 From Bryan Sayer To statalist@hsphsun2.harvard.edu Subject Re: st: RE: S-Curve/logistic curve regression Date Wed, 01 Apr 2009 13:47:29 -0400

Or maybe fitting splines with knots at the transition points. Stata has substantial spline fitting capabilities; however I do not.
```

Bryan Sayer
Health Data Systems and Analysis (HDSA) Center
Monday to Friday, 8:30 to 5:00
Phone: (614) 442-7369
FAX:  (614) 442-7329
BSayer@chrr.osu.edu
www.s-3.com

Nick Cox wrote:
```
```Some people would use -nl- here, but assuming that you can scale values
to values / maximum, you can still use a logit link, or linear
regression on a logit transformed variable. The only obvious problem is
if the bounds are attained, because logit(0) and logit(1) are
```
indeterminate. There are some related comments in
```SJ-8-1  gr0032  . . . . . . .  Stata tip 59: Plotting on any transformed
scale
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N.
J. Cox
Q1/08   SJ 8(1):142--145                                 (no
commands)
tip on how to graph data on a transformed scale

```
which explains how to plot continuous responses on a logit scale. Nick n.j.cox@durham.ac.uk
```Sven Wiese

I have a twodimensional dataset of two continious variables and want to
fit a regression to the data, but I want the outcome to be an s-Curve
(or logistic curve). I think it might be like fitting a polynomial to
the data, but as mentioned I want to fit an s-curve, which can be
expressed by the exponential function.
I am aware of the logistic regression, the difference is, that my
dependant variable is not binary.

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```
```*
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```