[R] Fitting a logistic regression

[Dani Valverde]

Thank you very much, Jun. This is what I was looking for.

Best!

Dani

On Wed, 2009-08-19 at 09:52 -0500, Jun Shen wrote:
> I would suggest a model with a baseline level, something like
> 
> nls(AMP~E0+(Emax-E0)*Time**gamma/(EC50**gamma+Time**gamma),data=your
> data,
> start=list(EC50=50,gamma=2,E0=0.2,Emax=1.2))->mod.test
> 
> AIC(mod.test) does improve. Hope this helps.
> 
> Jun
> 
> On Wed, Aug 19, 2009 at 5:04 AM, Dani Valverde
> <daniel.valverde at uab.cat> wrote:
>         Hello,
>         I have this data:
>          Time  AMP
>             0 0.2000000
>            10 0.1958350
>            20 0.2914560
>            40 0.6763628
>            60 0.8494534
>            90 0.9874526
>           120 1.0477692
>         
>         where AMP is the concentration of this metabolite with time.
>         If you plot
>         the data, you can see that it could be fitted using a logistic
>         regression. For this purpose, I used this code:
>         
>         AMP.nls <- nls(AMP~SSlogis(Time,Asym, xmid, scal), data =
>         concentrations,model=T)
>         
>         When plotting the fitted function, it seems that it fits quite
>         well at
>         the end of the time. However, at the beginning it seems that
>         the fit is
>         not so good. How can I achieve a better fit? Forgive me if it
>         is a
>         stupid question, but I am just starting with non linear
>         regression.
>         Thank you,
>         
>         Dani
>         --
>         [?]
>         
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> 
> 
> 
> -- 
> Jun Shen PhD
> PK/PD Scientist
> BioPharma Services
> Millipore Corporation
> 15 Research Park Dr.
> St Charles, MO 63304
> Direct: 636-720-1589
> 
-- 
Daniel Valverde Saubí

Grup de Biologia Molecular de Llevats
Facultat de Veterinària de la Universitat Autònoma de Barcelona
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