In a study comparing two diagnostic tests on the same patients, the agreement beyond chance is assessed using Cohen's kappa. If the observed agreement is 0.80 and the expected agreement by chance is 0.50, what is the kappa value?
- A 0.30
- B 0.60 ✓
- C 0.40
- D 0.67
Correct answer: B. 0.60
Explanation
Kappa = (Observed agreement − Expected agreement) / (1 − Expected agreement) = (0.80 − 0.50) / (1 − 0.50) = 0.30 / 0.50 = 0.60. A kappa of 0.60 represents substantial agreement; values above 0.80 are near-perfect. The formula corrects for agreement occurring purely by chance, unlike simple percent agreement.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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