Abstract
Model evaluation is used to derive model performance index that indicates practical values of prediction model. In practice, it occurs in the last step of the statistical modelling pipeline; and various types of model evaluation methods or strategies have been proposed in the literature. Iterative resampling strategy is believed to be more reliable than sampling approach like Kennardstone algorithm because it produces more than one test set to ensure better representativeness. Most of the iterative resampling methods available in commercial statistical software implement random resampling by default. This would produce biased estimator if the studied dataset is imbalanced,
Keywords: ATRFTIR spectrumpartial least squaresdiscriminant analysis (PLSDA)model validationforensic science
Introduction
Model evaluation is an important aspect along the statistical modelling pipeline, especially in the context of chemometrics. This is because it enables researchers to gain more insight about the potential of the prediction model in realworld settings. In fact, a wealth of model evaluation methods have been described in the literature ( Colins et al., 2014). Each is characterized by unique merits and pitfalls. Internal validation methods including
Recently, Lee, Liong, and Jemain ( 2018a) demonstrated the limitation of Kennardstone sampling algorithm against the iterative random resampling approaches to derive model performance index via external testing method. On the other hand, Molinaro, Simon, and Pfeiffer ( 2005) reported comparative performances between different resampling methods, including
Problem Statement
In practice, resampling strategies can be implemented randomly or systematically. The former allows the same sample to be resampled without restriction. It allows more possible number of combinations than the latter because systematic resampling ensures each sample only assigned as test set once. Random resampling is easy to run but could produce biased estimate if the dataset is imbalanced,
Research Questions
This work aims to find answer for two different but related research questions:
What is the difference between stratified random iterative sampling (RIS) and stratified iterative sampling (SIS) in external testing method?
Does the relative difference between stratified and random resampling strategies affected by the number of iterations and PLS components?
Purpose of the Study
The purpose of this work is to examine merits and pitfalls of stratified (SIS) and random (RIS) resampling in external testing method. The PLSDA technique and ATRFTIR spectrum were used to construct the prediction models.
Research Methods
All statistical analysis was performed using the R environment for statistical computing and graphics, version 3.5.0 ( R Core Team 2018). PLSDA was performed with ‘caret’ package ( Kuhn, 2019) and AsLS via ‘baseline’ package ( Liland & Mevik, 2015).
ATRFTIR Spectral Dataset
The primary spectral dataset consisting of 1361 samples and 5401 variables has been studied and reported elsewhere (Lee, Liong, & Jemain, 2018b, 2018c, 2019a, 2019b). The practical purpose of classification model is to predict brand of unknown pen inks using based on ATRFTIR spectrum of the ink entry. Table
Partial Least SquaresDiscriminant Analysis (PLSDA) Method
The dataset was split into 7:3 training and test sets using stratified (SIS) and random (RIS) iterative sampling strategies. Both strategies were repeated for
where
Model Validation
The dataset was split into 7:3 training and test sets using stratified (SIS) and random (RIS) iterative sampling strategies. Both strategies were repeated for
where
Comparison Analysis
The two resampling strategies were compared using descriptive and inferential statistics as well as exploratory tool, i.e. principal component analysis (PCA). The list of accuracy rates were used to compute mean
where
Findings
The performances of RIS and SIS were compared sequentially
In addition, the respective CV values reduce as the model includes more number of PLS components. It can be clearly seen from Table
Figure
In other words, this indicates both RIS and SIS are quite similar in performances. This provides evidence to state that stratification is not necessary in validating a colossal, multiclass and imbalanced spectral dataset. However, this is not in line with previous work stated stratified sampling shall be preferred in imbalanced dataset ( Kohavi, 1995). Such discrepancy can be partly explained by the fact that the studied dataset is of colossal size; and each group has been represented by rather large sample size. As a result, the relative class proportions show less deviations between the different drawn even simple random techniques has been adopted.
Conclusion
This work has compared empirical performances between random (RIS) and stratified (SIS) iterative sampling methods in PLSDA model. It is concluded that simple random resampling can be as reliable as stratified resampling in deriving model performance using imbalanced dataset if the dataset is of colossal size.
Acknowledgments
This work was supported by the CRIM, UKM (GUP2017043).
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Publication Date
30 March 2020
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9781802960808
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European Publisher
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81
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Business, innovation, sustainability, development studies
Cite this article as:
Lee, L. C. (2020). Comparison Of Stratified And Random Iterative Sampling In Evaluation Of PlsDa Model. In N. Baba Rahim (Ed.), Multidisciplinary Research as Agent of Change for Industrial Revolution 4.0, vol 81. (pp. 648656). European Publisher. https://doi.org/10.15405/epsbs.2020.03.03.75