Compute 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.
Labels assigned by the first annotator.
Labels assigned by the second annotator. The kappa statistic is symmetric, so swapping y1
and y2
doesn’t change the value.
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
or y2
are used. Note that at least one label in labels
must be present in y1
, even though this function is otherwise agnostic to the order of y1
and y2
.
Weighting type to calculate the score. None
means not weighted; “linear” means linear weighting; “quadratic” means quadratic weighting.
Sample weights.
The kappa statistic, which is a number between -1 and 1. The maximum value means complete agreement; zero or lower means chance agreement.
References
Examples
>>> from sklearn.metrics import cohen_kappa_score >>> y1 = ["negative", "positive", "negative", "neutral", "positive"] >>> y2 = ["negative", "positive", "negative", "neutral", "negative"] >>> cohen_kappa_score(y1, y2) 0.6875
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