[R] Need to replicate Boltzman Signmodial Curve fit from Graph Pad

peter dalgaard pdalgd at gmail.com
Tue Apr 23 18:55:49 CEST 2013

On Apr 23, 2013, at 18:45 , R. Michael Weylandt wrote:

> On Tue, Apr 23, 2013 at 3:55 PM, J J <rnoobier at gmail.com> wrote:
>> Hello useRs (please don't kill me),
>> I've fairly new to R having only a few months of playing around with R.
>> What little I've learned has been extremely useful.
>> If someone could point me as to how to replicate the Boltzman Sigmodial
>> curve fit as provided by Graphpad software I'd be eternally grateful.
>> Where  we currently use Graphpad for only this one function,its seems
>> highly inefficient for a $100 piece of software to be used for only one
>> function (which isn't nearly as bad as the company's pandemic reliance on
>> Excel for nearly everything else).
>> so anyway, what I'd normally do is take a set of data like this:
>> pH counts  3.8 968  5.0 1347  5.8 2867  6.6 9203  7.0 15817  7.4 20297  8.2
>> 31916  9.2 35756
>> then fit this to a Boltzman sigmodial in Graphpad. Graphpad spits out a
>> much longer set of vectors and also information about v50 and confidence
>> intervals etc (if anyone is familiar with that software). This is what i'd
>> like to replicate.
>> It might be that I just don't know what i'm doing,so feel free to call me
>> an idiot but any help is greatly appreciated!
> Being unfamiliar with the problem domain, I'd imagine that nls() would
> probably be what you're looking for. Does
> ? nls
> seem promising? If so, we can help you get started.

In particular, SSfpl looks tantalizingly similar to the Bolzmann sigmoidal (sic!) curve. 

Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

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