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