Variance, Covariance Matrix, Linear Regression, Standard Error, Confidence Interval.
Uncorrelated errors: The model’s errors are not correlated with each other: E(ϵ_i*ϵ_j|X) =0 when i != j When to be skeptical about the variance-covariance matrix If the above set of assumptions are violated, then the preceding set of derivations no longer hold, and equation (12) cannot be used to