XY Plot to compare predictions (same model / diferent instruments)

As we mention several times, plots help us to understand better what is happening. In the previous posts we are working with the shootout 2002 data in order to work with as many tools as possible we have in R to understand this data set and to make a model we can use to predict as better as possible a validation set.
Plotting the predictions of the Test set acquired in Instrument 2 with the model developed with the Training set of samples acquired in Instrument 1, versus the predictions of the test set acquired in instrument 1, can give us an idea that there is something more than a simple bias, and that we have to take into account a group of samples that behaves differently.
Lets see that plot:
1) We make the predictions of the Test1 set with Model 1 and stored it in:
  anl_tst1_mod1<-predict(mod1,ncomp=3,
+ newdata=data.frame(Y=I(Y.test),X=I(X1.test)))
2) We make the predictions of the Test2 set with Model 1 and stored it in:
  anl_tst2_mod1<-predict(mod1,ncomp=3,
+ newdata=data.frame(Y=I(Y.test),X=I(X2.test)))
3) Now we plot the predictions versus reference for anl_tst1_mod1
  plot(Y.test,anl_tst1_mod1,col="blue",ylim=c(150,240))
4) Now we write the script:
   par(new=TRUE)
5) Now we plot the predictions versus reference for anl_tst2_mod1
  plot(Y.test,anl_tst2_mod1,col="red",ylim=c(150,240))
6) Now we get this plot:

We can see that most of the samples behave similarly with a bias

 

If interested to follow this tutorial see also:

Working with the Shootout 2002 (NIR) in R

Plotting the predictions (Working with the Shootout 2012 NIR data in R)

Comparing Spectra and Coefficients (Shootout 2002 NIR with R)