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Re: st: RE: inflection point of sigmoid curves


From   Austin Nichols <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: inflection point of sigmoid curves
Date   Mon, 14 Jun 2010 17:17:15 -0400

Johannes Schmid--
Try these silly examples:

drawnorm x, mean(10) n(1000) clear
sort x
g y=(_n+1)/(_N+2)
reg x c.y##c.y##c.y
loc ybar=-2*_b[c.y#c.y]/(6*_b[c.y#c.y#c.y])
set obs `=_N+1'
replace y=`ybar' in l
ipolate x y, gen(px)
loc xbar=px[_N]
lpoly y x, nosc xli(`xbar')

webuse nhanes2, clear
ren  bpsystol y
ren age x
reg x c.y##c.y##c.y
loc ybar=-2*_b[c.y#c.y]/(6*_b[c.y#c.y#c.y])
set obs `=_N+1'
replace y=`ybar' in l
ipolate x y, gen(px)
loc xbar=px[_N]
lpoly y x, nosc xli(`xbar')


On Mon, Jun 14, 2010 at 3:12 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> I am not aware of a unique recipe for sigmoid curves. But in general fit
> a suitable function, apply calculus and plug in suitable parameter
> values.
>
> Nick
> n.j.cox@durham.ac.uk
>
> Johannes Schmid
>
> Is it possible to calculate the inflection point in sigmoid curves in
> STATA,
> and how can it be done?
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