> 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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