[R] Equation of a curve

Keith Jewell Keith.Jewell at campdenbri.co.uk
Fri Apr 4 10:11:26 CEST 2014

On 03/04/2014 16:26, Frances Cheesman wrote:
> Hi all,
> I have a number of bacterial growth curves I would like to find the
> equations for these and then integrate them to find the area under the
> curves for me to do stats on later.
> Is there any way I can do this in R?
> Thanks,
> Frances
> 	[[alternative HTML version deleted]]
Responding to the curve fitting question and passing over the 
integration issue...

It is quite common to use nls to fit equations to log(count) v time 
data. You'll have to choose an appropriate model, ideally as a self 
starting nls model. Of those included in the stats package you might 
consider SSfpl, SSgompertz, SSlogis and SSweibull.

But choice of a model is really a microbiological issue and all those 
models might be considered a little passe. Fitting this kind of 
sigmoidal model can be difficult unless the data is good.

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