Besides
of the true-predicted plots, which will be introduced in section
3.4, the root mean square errors (RMSE) are used for the validation of the
models in this work as it is one of the most common measures for the quality
of calibrations and predictions in chemometrics:
(22)
Thereby
is the
predicted concentration of the sample, yi
is the true concentration of the sample and N
is the total number of samples. The RMSE, which has the dimension and units
of the concentrations predicted, is a strict measure of the error as it penalizes
poor predictions by a quadratic term. For a relative measure of the error, the
relative RMSE, which is also sometimes misnamed standard error of prediction
(SEP) [41],[153],[154],
is used in this work: