Whenever we transfer
calibration databases from one instrument to be used in another type of
instrument, we use a type of standardization, scanning samples in both
instruments and after that we apply the standardization to the data base and
make a new calibration. We need to validate this equation with new samples from
the new instruments in order to see if the transfer was correct. But it is
usual that the equation can underfit or overfit the number of terms used in the
PLS Model. So whe we do the validation probably will in some cases some bias
effects or a high SEP than expected.
Is it good to develop the equation
again using the new spectra with lab values as an external set for validation
in order to decide the number of terms we will use in order to prevent the
calibration to be under-fitted or over-fitted.
Just look to the statistics
values of the SECV and SEV (SEP for the external validation set) and make your decision.
It is important to look at the
same time to the SEV and SEV(C) to check that we have not a bias in the
prediction of the validation test.
In the statistic list Win ISI recommends
14 terms for a moisture equation, but we can see clearly that is too much, so
we can take the decision to take less. What about four?. Just try.
