[R] Using known errors and error bars

[Sebastian Schubert]

> 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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