RE: [R] Help with predict.lm

From: Liaw, Andy <andy_liaw_at_merck.com>
Date: Tue 19 Apr 2005 - 22:53:24 EST


Will this help?
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/1202.html

[Found by RSiteSearch("calibration") in R-2.1.0.]

Andy

> From: Mike White
>
> Hi
> I have measured the UV absorbance (abs) of 10 solutions of a
> substance at
> known concentrations (conc) and have used a linear model to plot a
> calibration graph with confidence limits. I now want to predict the
> concentration of solutions with UV absorbance results given
> in the new.abs
> data.frame, however predict.lm only appears to work for new
> "conc" variables
> not new "abs" variables.
>
> I have search the help files and did find a similar problem
> in June 2000,
> but unfortunately no solution was offered.
> Any help and how to use predict.lm with the new "abs" data to
> predict "conc"
> with confidence limits would be appreciated.
>
> conc<-seq(100, 280, 20) # mg/l
> abs<-c(1.064, 1.177, 1.303, 1.414, 1.534, 1.642, 1.744,
> 1.852, 1.936,
> 2.046) # absorbance units
> lm.calibration<-lm(abs ~ conc)
> pred.w.plim <- predict(lm.calibration, interval="prediction")
> pred.w.clim <- predict(lm.calibration, interval="confidence")
> matplot(conc, cbind(pred.w.clim, pred.w.plim[,-1]),
> lty=c(1,2,2,3,3), type="l", ylab="abs", xlab=
> "conc mg/l")
> points(conc, abs, pch=21, col="blue")
>
> new.abs<-data.frame(abs=c(1.251, 1.324, 1.452))
>
> predict(calibration.lm, new.abs) # does not work
>
>
> Thanks
> Mike White
>
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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Apr 19 23:01:40 2005

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