Diagnosis II
Dr. Brent E. Faught, Ph.D. Assistant Professor Faculty of Applied Health Sciences Brock University St.Catharines, ON, Canada
Conditional Probabilities
Gold Standard (D +) (D -) (T Clinical Test (T -)
+)
True Positive False Negative
False Positive True Negative
Interpretation of Diagnostic Data
(D +) (D -)
B
P (T + D +) P (T + D –) OR
(T
+)
A
(T -)
C
D
A / (A + C) B / (B + D)
Interpretation of Diagnostic Data
(D +) (D -)
B
P (T – D +) P (T – D –)
OR
(T
+)
A
(T -)
C
D
C / (A + C) D / (B + D)
Interpretation of Diagnostic Data
(D +) (D -)
B
(T
+)
A
(A + D)
(T -)
C
D
Interpretation of Diagnostic Data
(D +) (D -)
B
(T +)
A
P ( D + T +)
OR
(T -)
C
D
__A__ (A + B)
Interpretation of Diagnostic Data
(D +) (D -)
B
(T +)
A
P( D - T -)
OR
(T -)
C
D
__D__ (C + D)
Revising Estimates of Diagnostic Test Performance
(D +) (T
+)
(D -)
228
1. Select an arbitrary sample size. 2. Based on prevalence, calculate the diseased individuals.
3. Calculate the disease-free individuals.
76
(T -)
4 80
1292 1520
4. Calculate D + based on fixed sensitivity. 5. Calculate D - based on fixed specificity.
1600
Effect of Prevalence on Predictive Values
100 80 60 40 20 0 5 20
Prevalence (%)
PV + PV -
50