Predictive Value Theory
The diagnostic value
of a procedure is defined by its sensitivity, specificity, predictive value
and efficiency. The formula are summarized below.

Test
Positive 
Test
Negative 
Disease
Present 
True
Positive (TP) 
False
Negative (FN) 
Disease
Absent 
False
Positive (FP) 
True
Negative (TN) 
SENSITIVITY:
Sensitivity of a test
is the percentage of all patients with disease present who have a positive
test.
__TP___ X 100
= Sensitivity (%)
TP + FN
SPECIFICITY:
Specificity of a test
is the percentage of all patients without disease who have a negative test.
__TN___ X 100
= Specificity (%)
FP + TN
PREDICTIVE VALUE:
The predictive value
of a test is a measure (%) of the times that the value (positive or negative)
is the true value, i.e. the percent of all positive tests that are true
positives is the Positive Predictive Value.
__TP___ X 100
= Predictive Value of a Positive Result (%)
TP + FP
__TN___ X 100
= Predictive Value Negative Result (%)
FN + TN
TEST EFFICIENCY:
The efficiency of a
test is the percentage of the times that the test give the correct answer
compared to the total number of tests.
____TP + TN______
X 100 = Efficiency of a Test Result (%)
TP + TN + FP + FN
