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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
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