Databases to develop Local calibrations has normally a high quantity of spectra with lab values, but we have to take care of them adding new sources of variance. This way we make them more robust and the standard prediction errors (SEP) decrease when we validate with future independent validation sets.
This was the case with a meat meal local database updated with 100 samples with protein values, and with new source of variation as: laboratories, reference methods (Kj, Dumas), providers, new instruments,...
After the LOCAL database update, a set of new samples was received with reference values and I have predicted this values with the Monitor function in Win ISI with the LOCAL database before (blue dots) and after the LOCAL update (red dots).
The errors decrease , specially for some types of samples, in an important way when validating with the new set of samples (new samples acquired after the updated Local calibration was installed in the routine software), so even if we have spectra from this instrument, labs, ...., this set has to be considered as an independent set.
I don´t give details of the statistics but this picture show the same samples predicted with the LOCAL calibration without update (in blue), and predicted with the LOCAL calibration update (in red), the improvement for the prediction for some samples is important, so the idea is to add this new samples and continuing monitoring the LOCAL database with future validation sets.