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Table 3 Contingency table for the observer agreement for cognitive impairment at cut- off -1SD

From: Validation of a culturally modified short form of the McCarthy Scales of Children’s Abilities in 6 to 8 year old Zimbabwean school children: a cross section study

Assessment at cut off – 1SD
Observer 1
Observer 2 Delayed Not Delayed Total
A B 13
True positive False positive  
9 4  
C D 88
False negative True negative  
9 79  
Total 18 83 101
  1. Sensitivity = A / A + C 9/18= 50%.
  2. Specificity = D / B + D 79/83=95%.
  3. Total Agreement = A + D / A + B + C + D (9+79)/101=87%.
  4. Positive Predictive Value = A / A + B 9/13=69%.
  5. Negative Predictive Value = D / C + D 79/88=89%.
  6. Over-referral = B / A + B + C + D 4/101=4%.
  7. Under-referral = C / A + B + C + D 9/101=9%.
  8. Likelihood ratio—positive = Sensitivity / (1 – specificity) 10.
  9. Likelihood ratio—negative = (1 – sensitivity) / specificity 0.53.