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Table 1 Deriving Sensitivity, Specificity, Positive/Negative Predictive Values for the common identification tests for S. aureus

From: Identification of Staphylococcus aureus: DNase and Mannitol salt agar improve the efficiency of the tube coagulase test

Test results Staphylococcus aureus Other staphylococci Total
Positive a b a + b
Negative c d c + d
Total a + c b + d (a + b) + (c + d) = n
  1. Where,
  2. a = True positives
  3. b = False positives
  4. c = False negatives
  5. d = True negatives
  6. Diagnostic sensitivity = d/(b + d)
  7. Diagnostic specificity = a/(a + c)
  8. Positive predictive value (PPV) = a/(a + b)
  9. Negative predictive value (NPV) = d/(d + c)
  10. n = 60