Metabolic And Cardiovascular Obesity Scores

Net Reclassification Index (NRI) Calculator

Clinical calculation support · Verify results before clinical use

Calculate reclassification improvement

Enter the proportions of events and non-events moving between risk categories after adding a predictor to the existing model.

—Total NRI

Study population

Enter the number of participants in each outcome group. These counts provide context and are used to estimate reclassified counts; NRI itself is calculated from within-group proportions.

Number of events (participants with outcome)

Enter a positive whole number.

Number of non-events (participants without outcome)

Enter a positive whole number.

Reclassification among participants with events

Use percentages of the event group, not percentages of the entire study population.

Events reclassified upward (%)

Enter a percentage from 0 to 100.

Events reclassified downward (%)

Enter a percentage from 0 to 100.

Reclassification among participants without events

Use percentages of the non-event group. Downward reclassification contributes positively to NRI; upward reclassification contributes negatively.

Non-events reclassified downward (%)

Enter a percentage from 0 to 100.

Non-events reclassified upward (%)

Enter a percentage from 0 to 100.

—Total NRI

Net reclassification improvement

Enter valid values to calculate

NRI is the sum of the event and non-event components.

Parameter	NRI (percentage points)	Estimated reclassified participants
Event NRI	—	—
Non-event NRI	—	—
Total NRI	—	Not applicable

The estimated counts are derived from the entered group sizes and percentages and may be fractional because the inputs are proportions.

Understanding the Net Reclassification Index

The Net Reclassification Index (NRI) describes how risk classifications change when a new marker or prediction model is compared with an existing model. It evaluates event and non-event groups separately.

Formula

Event NRI = proportion of events moving up − proportion of events moving down.

Non-event NRI = proportion of non-events moving down − proportion of non-events moving up.

Total NRI = event NRI + non-event NRI.

Interpreting the result

A positive NRI indicates a net movement in the direction conventionally considered appropriate: events upward and non-events downward.
A negative NRI indicates a net movement in the opposite direction.
An NRI near zero indicates little net directional improvement by this measure; it does not prove that two models are equivalent.
NRI is not a calibrated probability, an absolute risk estimate, or by itself proof of clinical utility.

Important methodological distinction

This calculator implements the component formula using the supplied group-specific reclassification proportions. It does not define risk categories, construct a reclassification table from patient-level data, calculate confidence intervals or p-values, or assess calibration, discrimination, or clinical net benefit. Confirm whether a category-based or category-free NRI is appropriate for the study design before interpreting results.

References

Pencina MJ, D’Agostino RB Sr, D’Agostino RB Jr, Vasan RS.Evaluating the added predictive ability of a new marker: From area under the ROC curve to reclassification and beyond. Statistics in Medicine. 2008;27(2):157–172. doi:10.1002/sim.2929.

Kerr KF, Wang Z, Janes H, McClelland RL, Psaty BM, Pepe MS.Net reclassification indices for evaluating risk prediction instruments: a critical review. Epidemiology. 2014;25(1):114–121. doi:10.1097/EDE.0000000000000018.