6.2 Variandes and standard Errors of Ordinary Least Squares (OLS) Estimators Study the sampling variability ofOLS estimators The variances and standard errors of the ols estimators var(b1=2X.02 (b1)=var(b1) va(b2×2 se(b2)=/var(b (6.7) 02 IS an estimator of o 2 (6.8) 2 n-2 (6.9) ∑e2=RSs( (residual sum of squares=∑(YrY1) degrees of freedom6.2 Variandes and Standard Errors of Ordinary Least Squares（OLS）Estimators ◼ ——Study the sampling variability of OLS estimators. ◼ The variances and standard errors of the OLS estimators: var(b1 )= ·σ2 (6.4) se(b1 ) = (6.5) var(b2 )= (6.6) se(b2 ) = (6.7) is an estimator of σ2 (6.8) (6.9) ∑ei 2=RSS(residualsum of squares) =∑（Yi -Yi）2 n-2……..degrees of freedom   2 i 2 i n X X var(b ) 1  2 i 2 X σ var(b ) 2 σ ˆ 2 n 2 e σ 2 i 2 − ˆ =  2 σ ˆ = σ ˆ