Predictive accuracy is a measure of diagnostic power of the test.
Predictive accuracy of a screening test depends on disease prevalence, sensitivity and specificity of the test.
Sensitivity
The ability of the test to correctly identify patients with the disease.
= True positives / Diseased individuals
Specificity
The ability of the test to correctly identify individuals without the disease
= True negatives / Healthy individuals
Positive Predictive Value - PPV
The likelihood that an individual with positive test result actually has the disease.
It is the proportion of true positives in test positives.
PPV = True positives / Test positives
PPV = True positives / (True positives + False positives)
Negative Predictive Value - NPV
The likelihood that an individual with negative test result is actually disease free.
It is the proportion of true negatives in test negatives.
NPV = True negatives / Test negatives
NPV = True negatives / (True negatives + False negatives)
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