[R] Help with predict.lm
TEMPL Matthias
Matthias.Templ at statistik.gv.at
Tue Apr 19 14:56:45 CEST 2005
> 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
lm.calibration
predict(lm.calibration, new.abs)
Is this the reason for not working?
Best,
Matthias
>
>
> Thanks
> Mike White
>
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