What does R2 mean for linear regression? R2 is the proportion of variability in the predictors that is explained by the outcome Y in a regression model. R2 is the likelihood of observing the data, penalized by the number of predictors in the model. R2 is the correlation between the outcome Y and a single predictor X, controlling for all other predictors. R2 is the correlation between the outcome Y and a single predictor X. 0 R2 is the proportion of variability in the outcome Y that is explained by the predictors in a regression model