cohens_kappa.py

import numpy as np


def calc_cohens_kappa(matrix):
    p0 = (matrix[0][0] + matrix[1][1]) / matrix.sum()
    pyes = (matrix[0].sum() / matrix.sum()) * ((matrix[0][0] + matrix[1][0]) / matrix.sum())
    pno = (matrix[1].sum() / matrix.sum()) * ((matrix[0][1] + matrix[1][1]) / matrix.sum())
    pe = pyes + pno
    k = (p0 - pe) / (1 - pe)
    print(k)


calc_cohens_kappa(np.array([[20, 5], [10, 15]]))
calc_cohens_kappa(np.array([[45, 15], [25, 15]]))
calc_cohens_kappa(np.array([[25, 35], [5, 35]]))

calc_cohens_kappa(np.array([[37, 14], [17, 32]]))
calc_cohens_kappa(np.array([[65, 8], [7, 20]]))
calc_cohens_kappa(np.array([[90, 4], [5, 1]]))


"""
κ < 0           poor agreement
0 < κ < 0.2     slight agreement
0.21 < κ < 0.4  fair agreement
0.41 < κ < 0.6  moderate agreement
0.61 < κ < 0.8  substantial agreement
0.81 < κ < 1    (almost) perfect agreement
"""