[source] # RMSE The Root Mean Squared Error (RMSE) is equivalent to the standard deviation of the error residuals in a regression problem. Since RMSE is just the square root of the [MSE](mean-squared-error.md), RMSE is also sensitive to outliers because larger errors have a disproportionately large effect on the score. $$ {\displaystyle \operatorname {RMSE} = {\sqrt{ \frac {1}{n} \sum _{i=1}^{n}(Y_{i}-{\hat {Y_{i}}})^{2}}}} $$ !!! note In order to maintain the convention of *maximizing* validation scores, this metric outputs the negative of the original score. **Estimator Compatibility:** Regressor **Score Range:** -∞ to 0 ## Parameters This metric does not have any parameters. ## Example ```php use Rubix\ML\CrossValidation\Metrics\RMSE; $metric = new RMSE(); ```