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

 Sensitivity = A / A + C 9/18= 50%.
 Specificity = D / B + D 79/83=95%.
 Total Agreement = A + D / A + B + C + D (9+79)/101=87%.
 Positive Predictive Value = A / A + B 9/13=69%.
 Negative Predictive Value = D / C + D 79/88=89%.
 Overreferral = B / A + B + C + D 4/101=4%.
 Underreferral = C / A + B + C + D 9/101=9%.
 Likelihood ratio—positive = Sensitivity / (1 – specificity) 10.
 Likelihood ratio—negative = (1 – sensitivity) / specificity 0.53.