sklearn.metrics.cohen_kappa_score — scikit-learn 0.20.4 documentation (original) (raw)
sklearn.metrics. cohen_kappa_score(y1, y2, labels=None, weights=None, sample_weight=None)[source]¶
Cohen’s kappa: a statistic that measures inter-annotator agreement.
This function computes Cohen’s kappa [1], a score that expresses the level of agreement between two annotators on a classification problem. It is defined as
\[\kappa = (p_o - p_e) / (1 - p_e)\]
where \(p_o\) is the empirical probability of agreement on the label assigned to any sample (the observed agreement ratio), and \(p_e\) is the expected agreement when both annotators assign labels randomly.\(p_e\) is estimated using a per-annotator empirical prior over the class labels [2].
Read more in the User Guide.
| Parameters: | y1 : array, shape = [n_samples] Labels assigned by the first annotator. y2 : array, shape = [n_samples] Labels assigned by the second annotator. The kappa statistic is symmetric, so swapping y1 and y2 doesn’t change the value. labels : array, shape = [n_classes], optional List of labels to index the matrix. This may be used to select a subset of labels. If None, all labels that appear at least once iny1 or y2 are used. weights : str, optional List of weighting type to calculate the score. None means no weighted; “linear” means linear weighted; “quadratic” means quadratic weighted. sample_weight : array-like of shape = [n_samples], optional Sample weights. |
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| Returns: | kappa : float The kappa statistic, which is a number between -1 and 1. The maximum value means complete agreement; zero or lower means chance agreement. |
References
| [1] | (1, 2) J. Cohen (1960). “A coefficient of agreement for nominal scales”. Educational and Psychological Measurement 20(1):37-46. doi:10.1177/001316446002000104. |
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| [2] | (1, 2) R. Artstein and M. Poesio (2008). “Inter-coder agreement for computational linguistics”. Computational Linguistics 34(4):555-596. |
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| [3] | Wikipedia entry for the Cohen’s kappa. |
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