(2)Including an irrelevant variable in the model (the case of overfitting) AThe coefficients of variables are unbiased as well as consistent of the true model o The error variance is correctly estimated x The usual hypothesis-testing procedure is still valid But the estimated variances of the coefficients are less precise because the standard errors are larger and the confidence intervals tend to be wider（2）Including an irrelevant variable in the model (the case of overfitting) ☆The coefficients of variables are unbiased as well as consistent of the true model ； ☆The error variance is correctly estimated； ☆ The usual hypothesis-testing procedure is still valid. But the estimated variances of the coefficients are less precise because the standard errors are larger and the confidence intervals tend to be wider