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Table 4 Comparisons of eight different pretreatment approaches in the prediction of adjusted rubber

From: A high-throughput quantification of resin and rubber contents in Parthenium argentatum using near-infrared (NIR) spectroscopy

Cross validation

DRY + IRR

DRY

IRR

\({\text{R}}_{\text{CV}}^{2}\)

RMSECV

RMSEC

RMSECV/RMSEC

F

 

\({\text{R}}_{\text{CV}}^{2}\)

RMSECV

RMSEC

RMSECV/RMSEC

F

 

\({\text{R}}_{\text{CV}}^{2}\)

RMSECV

RMSEC

RMSECV/RMSEC

F

 

No preprocessing

0.652

0.899

0.885

1.016

7

 

0.661

0.898

0.868

1.035

7

 

0.632

0.794

0.776

1.022

7

 

Smoothing

0.653

0.897

0.885

1.013

7

 

0.665

0.892

0.868

1.028

7

 

0.629

0.796

0.777

1.026

7

 

Smoothing + normalization

0.642

0.912

0.900

1.013

7

 

0.682

0.870

0.853

1.021

7

 

0.614

0.813

0.794

1.023

7

 

Smoothing + baseline + normalization

0.658

0.890

0.883

1.008

7

 

0.658

0.900

0.868

1.037

7

 

0.625

0.801

0.781

1.025

7

 

SNV

0.660

0.890

0.878

1.013

7

 

0.684

0.866

0.846

1.024

7

 

0.631

0.794

0.776

1.023

7

 

SNV + DT

0.667

0.879

0.870

1.011

7

 

0.699

0.846

0.818

1.034

7

 

0.641

0.784

0.766

1.023

7

 

SNV + DT + 1st derivative

0.683

0.857

0.846

1.014

5

 

0.718

0.819

0.776

1.056

7

 

0.667

0.755

0.740

1.020

4

 

SNV + DT + 2nd derivative

0.733

0.788

0.731

1.078

7

 

0.756

0.763

0.661

1.153

7

 

0.728

0.683

0.599

1.140

7

 

External validation

\({\text{R}}_{\text{P}}^{2}\)

RMSEP

RMSEC

RMSEP/RMSEC

F

RPD

\({\text{R}}_{\text{P}}^{2}\)

RMSEP

RMSEC

RMSEP/RMSEC

F

RPD

\({\text{R}}_{\text{P}}^{2}\)

RMSEP

RMSEC

RMSEP/RMSEC

F

RPD

SNV + DT + 2nd derivative

0.756

0.753

0.731

1.030

7

2.024

0.780

0.724

0.661

1.095

7

2.128

0.755

0.647

0.618

1.047

6

2.019

  1. Smoothing: median filter smoothing; Normalization: normalization by mean; Baseline: offset and linear baseline correction; SNV: standard normal variate; DT: de-trending, 2nd polynomial; Savitzky–Golay 1st derivative, 2nd polynomial, 23 smoothing points; Savitzky–Golay 2nd derivative, 2nd polynomial, 23 smoothing points
  2. R2, coefficient of determination; RMSECV, root mean squared error of cross validation; RMSEC, root mean squared error of calibration; CV, cross validation; EV, external validation; F, number of factors (latent values) used in calibration; RPD, ratio of performance over prediction)