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Table 2 SMI vs. headache specialist's clinical diagnoses "gold standard"

From: Diagnosing migraine in research and clinical settings: The validation of the Structured Migraine Interview (SMI)

  Clinical Diagnoses Total
SMI Diagnoses Migraine No Migraine  
Migraine 138 (a) 5 (b) 143
No Migraine 20 (c) 7 (d) 27
Total 158 12 170
  1. Sensitivity: a/(a+c) = 138/138+20 = 138/158 = 0.87
  2. Specificity: d/(b+d) = 7/5+7 = 7/12 = 0.58
  3. Misclassification rate: b+c/(a+b+c+d) = 5+20/(138+5+20+7) = 25/170 = 0.15
  4. Positive predictive value: a/(a+b) = 138/(138+5) = 138/143 = 0.97
  5. Negative predictive value: d/(c+d) = 7/(20+7) = 7/27 = 0.26