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Cross validation setup

In the multivariate calibration wizard cross validation can be used with PLS calibration models.

This validation process allows automatic quality control of the derived calibration model by keeping some samples out of the calibration and only use them for prediction. This procedure is repeated during calculation of the calibration model until all samples have been kept out once. The residual variance is then calculated from the prediction residuals showing the overall quality of the model.

In segmented cross validation, the samples are divided into several groups. During calculation of the calibration model each group or segment is kept out at a time. There are as many calculations for the calibration as segments. This procedure will allow to make predictions on all samples. A final calibration is then calculated including all samples.

The cross validation method can be selected in the following dialog. Parameters for the selected method must be configured here.

Contents

The dialog contains a drop down box for selection of the cross validation method applied in calibration process.

With segmented cross validation methods, two additional parameters for segment adjustment are available:

  • Number of segments
    This number indicates the number of groups. All samples will be evenly divided and assigned to one of the groups. The maximum number of groups is equal to the number of samples.

  • Samples per segment
    The user selects the maximum number of samples assigned to a segment or group. The number of segments is calculated automatically according to the specified number of samples per segment.

A list box in the lower part of the dialog shows current settings and assignment of samples per segment.

Cross validation methods

The following cross validation methods can be configured:

None

The cross validation is deactivated.

Full

The full cross validation considers all samples during calculation of the calibration model except one. Only one sample at a time is kept out respectively. There are as many calibration calculations as samples are included.

Random

All samples are randomly divided into a given number of segments. Either the number of segments or the number of samples per segment can be adjusted in the dialog. Samples are randomly assigned and the resulting assignment is shown in the list box below.

Systematic 123123123

All samples are assigned systematically in a pre-defined order following the number of samples per segment.

Example:

Systematic 111222333

All samples are assigned systematically in a pre-defined order following the number of samples per segment.

Example: