What Is Net Reclassification Improvement (NRI)? A Simple Guide with Examples

🧠 What Is NRI?

The Net Reclassification Improvement (NRI) is a way to measure how much better a new diagnostic model or test is at correctly classifying people compared to an old model.

It tells us whether the new model moves people into more appropriate risk categories:

• Higher probability for those with the disease (D = 1)

• Lower probability for those without the disease (D = 0)

  
  

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📐 The Formula Explained

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🔢 An Example with Numbers

Suppose we apply a new diagnostic model to 100 people:

• 40 have the disease (D=1)

• 60 do not (D=0)

In comparison to the old model, here’s what happened:

🎯 Interpretation:

• The new model improved net classification by 30% overall.

• That means it correctly moved more people into the “right direction” than the wrong one.
  

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🔍 Summary Table

Direction of Movement	Group	Effect on Accuracy	Good or Bad?
Upward	D = 1	More likely to detect	✅ Good
Downward	D = 1	Misses diagnosis	❌ Bad
Downward	D = 0	Avoids overtreatment	✅ Good
Upward	D = 0	Increases false positives	❌ Bad