U01.21.018 Positive Predictive Value (PPV)

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Learning Objective:
Understand and apply the formula for PPV, which measures the probability that a patient with a positive test result actually has the disease.

Formula:

PPV = \frac{TP}{TP + FP}

Explanation:

  • TP (True Positives): Patients who have the disease and test positive.
  • FP (False Positives): Patients who do not have the disease but test positive.
  • PPV indicates how likely a positive test result truly reflects the disease.

Interpretation:

  • High PPV → most positive results are true positives
  • Influenced by disease prevalence: higher prevalence → higher PPV

Example:

If a test identifies 90 true positives and 10 false positives:
TP = 90, FP = 10

PPV = \frac{90}{90 + 10} = \frac{90}{100} = 0.9

✅ Answer: PPV = 90%

Activity:

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