sklearn.metrics
.cohen_kappa_score¶
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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 [R202], 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 [R203].
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
andy2
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 in
y1
ory2
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.
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
[R202] (1, 2) J. Cohen (1960). “A coefficient of agreement for nominal scales”. Educational and Psychological Measurement 20(1):37-46. doi:10.1177/001316446002000104. [R203] (1, 2) R. Artstein and M. Poesio (2008). “Inter-coder agreement for computational linguistics”. Computational Linguistics 34(4):555-596. [R204] Wikipedia entry for the Cohen’s kappa.