Re: [R] Using known errors and error bars

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From: Sebastian Schubert (Sebastian-Schubert@gmx.de)
Date: Tue 11 May 2004 - 05:32:07 EST


Message-id: <32159.1084217527@www11.gmx.net>


> What do you actually know?
>
> You don't have `known errors', as if you did you could correct the
>values.
> I doubt if you actually have a known range, more likely a standard error
> or a confidence interval. (If you think you do have a known range, how
> do
> you know?)
 
Firstly, I must admit that I do not know much about statistics (and, in
addition, do not always know the right English terms). I had to measure an
electric potential difference and I know from the technical dates of the
device that the confidence interval (?) is 5% of the maximum value on the
scale (eg I measured 1.2V on a 2V scale so I have (1.2+-0.1)V).
 
 
> And if A is not known exactly, linear regression is not fully
appropriate.
>
> If you know standard errors, then you need a homoscedastic
> errors-in-variables formulation. One early account is
>
> Ripley, B. D. and Thompson, M.(1987) Regression techniques for the
> detection of analytical bias. Analyst 112, 177-183.
>
> and its Fortran program is still available, and although I have never
> coded it in R, I believe others have.
 
I will look for it.
 
> > How can I put error bars for A and B in the plot (like Excel is
capable
> > of)?
>
> Many ways, for example using arrows() or plotCI in package gregmisc.
 
I tried the last one and it worked well.
Thank you for your advice
Sebastian Schubert

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