BUCHI NIRCal - Manual (Page 203)

Chemometrics
NIRCal 5.5 Manual, Version A 203
3.18.88 V-Set BIAS
Description BIAS of the validation set spectra.
Use Judge the V-Set results.
Method PCR / PLS
Matrices ID 26
Tip Should be as close to zero as possible.
Details This is a value for accuracy. Available in the calibration protocol.
Formula
Related Topic C-Set BIAS
The V-Set Bias provides information on the average deviation of the predicted values from the true
values. This value gives information on a systematic deviation of the calibration and therefore should
be as close to zero as possible.
The C-Set Bias is zero by definition.
3.18.89 V-Set PRESS
Description Validation Set: Predicted Residual Error Sum Square
Use To estimate the number of PCs. Compare it with the C-Set PRESS.
Method PCR / PLS
Matrices ID 22
Tip Graphics / V-Set Statistics / PRESS
Details Shows the validation set PRESS in function of the number of PCs.
Formula
Related Topic C-Set PRESS
This function calculates the error sum square as a function of the number of PCs. The term „residual“
here refers to the difference between the predicted values and the reference values.
The optimum number of PC is always given by the smallest number of PC where the PRESS function
for the calibration and for the validation set is approximately equal and minimal.
If the error of the prediction diminishes only very slightly by the addition of another PC, it is not worth
while to add that PC. This is because higher PCs with little influence will often result in a poorer
reproducibility or stability of the calibration.