The Concordance Index Calculator is a helpful tool in statistics and survival analysis that measures the predictive accuracy of models. The C-index evaluates how well predicted risks agree with actual outcomes and is widely used in fields like healthcare, machine learning, and research.
Formula
The formula used for calculating the Concordance Index is:
C-index = (Observed value minus Expected value) divided by the Total number of observations
How to Use
- Enter the observed value (O).
- Enter the expected value (E).
- Enter the total number of observations (N).
- Click the “Calculate” button to see the Concordance Index result.
Example
Let’s say the observed value is 75, expected value is 60, and total observations are 100.
C-index = (75 – 60) / 100 = 0.15
FAQs
- What is a Concordance Index?
It measures how well predicted outcomes match actual outcomes in a ranking order. - What does a C-index of 1 mean?
It means perfect prediction — all outcomes are perfectly ranked. - Is a higher Concordance Index better?
Yes, higher values indicate better predictive power. - What is a good C-index score?
A score above 0.7 is generally considered acceptable, and above 0.8 is considered strong. - What if the total number of observations is zero?
You cannot divide by zero; make sure the total is greater than zero. - Can this be used for survival analysis?
Yes, the C-index is commonly used in survival analysis to evaluate model performance. - Can I use decimal numbers?
Yes, the calculator supports decimal values. - What fields use the Concordance Index?
It’s used in medicine, statistics, machine learning, and social science research. - Is this calculator accurate?
Yes, it uses the standard formula and rounds results to four decimal places. - Can the C-index be negative?
Yes, a negative value implies that the model performs worse than random chance. - What is the range of the C-index?
Typically from 0 to 1, but it may be negative in rare cases of poor model performance. - Is it useful for classification problems?
It’s more suitable for ranking predictions than binary classifications. - Can this calculator be used offline?
Yes, just save the HTML code and use it in any browser. - Does this calculator store any data?
No, it processes everything locally and stores nothing. - How do I reset the calculator?
Just refresh the page or clear the input fields. - Can it help with regression models?
It’s better suited for survival and ranking models than standard regression. - Is this tool free?
Yes, it’s completely free and open to use. - Can I share the results?
Yes, simply copy and paste the result. - Does the order of input matter?
Yes, always enter observed minus expected. - Why is the result in decimals?
The C-index is typically represented as a decimal between 0 and 1 for precision.
Conclusion
The Concordance Index Calculator is an essential tool for analysts and researchers working with predictive models. By offering a quick and accurate way to assess how well your model ranks outcomes, it provides valuable insights into performance, aiding better decision-making across various fields.