Cited by 6,143Imbalanced Data Classification TechniquesMachine Learning and Data ClassificationStatistical Methods in Epidemiology

The DOI matches its Crossref record; 101 of the 104 references it cites were found in a registry or an index; none of the 27 sources its claims cite is checked for support yet.

The advantages of the Matthews correlation coefficient (MCC) over F1 score and accuracy in binary classification evaluation

Open access
Chicco, Davide, Jurman, Giuseppe·2020·BMC Genomics

Abstract

Background: To evaluate binary classifications and their confusion matrices, scientific researchers can employ several statistical rates, accordingly to the goal of the experiment they are investigating. Despite being a crucial issue in machine learning, no widespread consensus has been reached on a unified elective chosen measure yet. Accuracy and F 1 score computed on confusion matrices have been (and still are) among the most popular adopted metrics in binary classification tasks. However, these statistical measures can dangerously show overoptimistic inflated results, especially on imbalanced datasets. Results: The Matthews correlation coefficient (MCC), instead, is a more reliable statistical rate which produces a high score only if the prediction obtained good results in all of the four confusion matrix categories (true positives, false negatives, true negatives, and false positives), proportionally both to the size of positive elements and the size of negative elements in the dataset. Conclusions: In this article, we show how MCC produces a more informative and truthful score in evaluating binary classifications than accuracy and F 1 score, by first explaining the mathematical properties, and then the asset of MCC in six synthetic use cases and in a real genomics scenario. We believe that the Matthews correlation coefficient should be preferred to accuracy and F 1 score in evaluating binary classification tasks by all scientific communities.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper argues that the Matthews correlation coefficient (MCC) is a more reliable metric than accuracy and F1 score for evaluating binary classifications, especially on imbalanced datasets, because MCC requires good performance on both positive and negative classes. It supports this through mathematical analysis, six synthetic use cases, and a real colon cancer gene expression experiment.

Key findings

  • In six synthetic use cases, MCC was the only metric that correctly indicated the prediction problem in all six. For Use case A1 (91 positives, 9 negatives; TP=90, FN=1, TN=0, FP=9), accuracy=0.90 and F1=0.95, but MCC=−0.03. For Use case C2 (11 positives, 89 negatives; TP=2, FN=9, TN=88, FP=1), accuracy=0.90, F1=0.29, and MCC=+0.31.
  • Correlation analysis over all possible confusion matrices showed MCC and accuracy were strongly correlated, while F1 correlated less than 0.8 with the other two measures. For N=1000, PCC(MCC,F1)=0.775982, PCC(MCC,accuracy)=0.921030, and PCC(accuracy,F1)=0.778652.
  • In the colon cancer gene expression dataset (2,000 gene probesets, 62 patients: 22 healthy controls and 40 colon cancer; 35.48% negatives, 64.52% positives), rankings differed by metric. MCC ranked gradient boosting top (MCC=+0.55, TP rate=0.85, TN rate=0.69), while F1 and accuracy ranked k-NN top (F1=0.87, accuracy=0.80, TP rate=0.92, TN rate=0.52). Radial SVM had F1=0.75 and accuracy=0.67 but TN rate=0.40 and MCC=+0.29.
  • MCC produces a high score only if the classifier correctly predicts the majority of positive and negative instances; F1 is independent of true negatives and is not symmetric for class swapping, while accuracy can be overoptimistic on imbalanced datasets.

Methods

  • The paper defines accuracy, MCC, and F1 score mathematically, explores their relationships using Pearson correlation coefficient over all possible confusion matrices for N≥10 up to 1000, and plots all 21,084,251 possible confusion matrices for a 500-sample dataset on the MCC/F1 plane.
  • Six synthetic use cases vary class balance and imbalance with specified confusion matrices to compare metric behavior.
  • The real genomics experiment uses colon cancer gene expression data from Alon et al. via the plsgenomics R package, applying gradient boosting, decision tree, k-nearest neighbors, linear SVM, and radial SVM. Training/test splits were 80/20 or 60/20/20 with validation for hyperparameter grid search; experiments were repeated ten times and averaged for MCC, F1, accuracy, TP rate, and TN rate.

Limitations

  • The paper states that additional comparisons with other rates such as Cohen’s Kappa, Cramér’s V, and K measure would have provided further information, but the authors focused on accuracy and F1 because they are more commonly used in biomedical machine learning studies.
  • The paper notes that MCC can be undefined when a whole row or column of the confusion matrix is zero, and handles these cases via an approximation using an arbitrarily small value ε; it also cites situations where MCC can display large fluctuations due to imbalanced outcomes.
  • Evident from the text: the real-world validation uses a single colon cancer gene expression dataset, the six use cases are synthetic, and Table 5 excludes standard deviations to keep the table simple.

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Integrity signals

Registry

Crossref · 10.1186/s12864-019-6413-7

Cites

101 of 101 references verified0 citation errors · 0 not checkable

Statistics

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Figures

Fig. 1 Relationship between MCC and F1 score. Scatterplot of all the 21 084 251 possible confusion matrices for a dataset with 500 samples on the MCC/ F1 plane. In red, the (−0.04, 0.95) point corresponding to use case A1
Fig. 1 Relationship between MCC and F1 score. Scatterplot of all the 21 084 251 possible confusion matrices for a dataset with 500 samples on the MCC/ F1 plane. In red, the (−0.04, 0.95) point corresponding to use case A1CC BY · PubMed Central
Fig. 2 Use case A1 — Positively imbalanced dataset. a Barplot representing accuracy, F1, and normalized Matthews correlation coefficient (normMCC = (MCC + 1) / 2), all in the [0, 1] interval, where 0 is the worst possible score and 1 is the best possible score, applied to the Use case A1 positively imbalanced dataset. b Pie chart representing the amounts of true positives (TP), false negatives (FN), true negatives (TN), and false positives (FP). c Pie chart representing the dataset balance, as the amounts of positive data instances and negative data instances
Fig. 2 Use case A1 — Positively imbalanced dataset. a Barplot representing accuracy, F1, and normalized Matthews correlation coefficient (normMCC = (MCC + 1) / 2), all in the [0, 1] interval, where 0 is the worst possible score and 1 is the best possible score, applied to the Use case A1 positively imbalanced dataset. b Pie chart representing the amounts of true positives (TP), false negatives (FN), true negatives (TN), and false positives (FP). c Pie chart representing the dataset balance, as the amounts of positive data instances and negative data instancesCC BY · PubMed Central

Verification

Claims the paper makes

29 Own interpretation · 28 Own result · 15 Not checked yet · 13 No basis given

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  • Probably not a substantial claim. 15
  • The quote only partly states this claim. 5
  • It may state two separate claims as one. 36
44 of 44
  • The paper relies on this without support.

    Accuracy and F1 score are the most common metrics used for binary classification in machine learning.

    “We decided to focus on accuracy and F1 score because they are the most common metrics used for binary classification in machine learning.”
  • The paper relies on this without support.

    The synthetic use cases are realistic representations of binary classification scenarios.

    “here we describe some synthetic, realistic scenarios where MCC results are more informative and truthful than the other two measures analyzed.”
  • The paper relies on this without support.

    Accuracy and F1 score are more commonly used in machine learning studies related to biomedical applications than other rates.

    “because accuracy and F1 score are more commonly used in machine learning studies related to biomedical applications.”
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Citations

Cites

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Research works printed but not linked: 7

  1. Akosa JS. Predictive accuracy: a misleading performance measure for highly imbalanced data. In: Proceedings of the SAS Global Forum 2017 Conference. Cary, North Carolina: SAS Institute Inc.: 2017. p. 942–2017.
  2. Guilford JP. Psychometric Methods. New York City: McGraw-Hill; 1954.
  3. van Rijsbergen CJ, Joost C. Information Retrieval. New York City: Butterworths; 1979.
  4. Sasaki Y. The truth of the F-measure. Teach Tutor Mater. 2007; 1(5):1–5.
  5. Dubey A, Tarar S. Evaluation of approximate rank-order clustering using Matthews correlation coefficient. Int J Eng Adv Technol. 2018; 8(2):106–13.
  6. Suresh Babu N. Various performance measures in binary classification – An overview of ROC study. Int J Innov Sci Eng Technol. 2015; 2(9):596–605.
  7. Ferri C, Hernández-Orallo J, Flach PA. A coherent interpretation of AUC as a measure of aggregated classification performance. In: Proceedings of ICML 2011 – the 28th International Conference on Machine Learning. Norristown: Omnipress: 2011. p. 657–64.

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Metadata

Authors
Chicco, D., & Jurman, G.
Affiliations
  • Krembil Research Institute (CA)
  • Fondazione Bruno Kessler (IT)
Corresponding author
Chicco, Davide
Venue
BMC Genomics
Published
2020-01-02
Volume
21
Issue
1
Pages
6-6
ISSN
1471-2164 (ISSN-L)
OpenAlex
W2999309192
Cited by
6,143
References
104
Citations by year
2026: 1118 · 2025: 1152 · 2024: 1060 · 2023: 1032 · 2022: 883 · 2021: 682 · 2020: 211
FWCI
276.55
Type
journal article
Language
en
Open access
Locations
  • BMC Genomics (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • BOA (University of Milano-Bicocca) (submittedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
  • Iris (University of Trento) (submittedVersion)
Funders
University of Toronto
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Imbalanced Data Classification Techniques
  • Physical Sciences › Computer Science › Artificial Intelligence › Machine Learning and Data Classification
  • Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Epidemiology
Keywords
Matthews correlation coefficient, F1 score, accuracy, confusion matrix, class imbalance, classification metrics
MeSH terms
Machine Learning, Correlation of Data, Algorithms, Data Interpretation, Statistical, Computational Biology

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