Concordance Index Calculator

The concordance index (C-index) is a metric commonly used to evaluate the predictive accuracy of survival models in statistical analysis, such as Cox proportional hazards models. It assesses how well the predicted ranks of subjects correspond to their true ranks. A C-index of 1.0 indicates perfect prediction, while 0.5 represents random predictions.

Calculation Method

The C-index is calculated by determining the ratio of concordant pairs (where the predicted and actual rankings match in order) to permissible pairs (those that can be compared).

Example Usage Scenarios

The concordance index is frequently used in medical research and machine learning to validate predictive models, especially in scenarios where survival or time-to-event outcomes are of interest.

Common FAQs

1. What does a C-index of 0.7 mean?

   • A C-index of 0.7 indicates that 70% of the time, the model correctly predicts the ranking order of events.

2. When should I use the concordance index?

   • Use the C-index when evaluating survival models or any model where the ranking of predictions is more important than the actual values.