What issues does heteroskedasticity cause?
Heteroskedasticity has serious consequences for the OLS estimator. Although the OLS estimator remains unbiased, the estimated SE is wrong. Because of this, confidence intervals and hypotheses tests cannot be relied on. In addition, the OLS estimator is no longer BLUE.
What is heteroscedasticity impact model estimate?
While heteroscedasticity does not cause bias in the coefficient estimates, it does make them less precise. Lower precision increases the likelihood that the coefficient estimates are further from the correct population value. Heteroscedasticity tends to produce p-values that are smaller than they should be.
Why is heteroscedasticity a problem in OLS regression?
Heteroscedasticity is a problem because ordinary least squares (OLS) regression assumes that all residuals are drawn from a population that has a constant variance (homoscedasticity). To satisfy the regression assumptions and be able to trust the results, the residuals should have a constant variance.
When to test for homoscedasticity in OLS model?
If the OLS model is well-fitted there should be no observable pattern in the residuals. The residuals should show no perceivable relationship to the fitted values, the independent variables, or each other. A visual examination of the residuals plotted against the fitted values is a good starting point for testing for homoscedasticity.
How to check for heteroskedasticity in multivariate OLS?
One way to visually check for heteroskedasticity is to plot predicted values against residuals This works for either bivariate or multivariate OLS. If heteroskedasticity is suspected to derive from a single variable, plot it against the residuals
What should the residuals be for heteroscedasticity?
In this tutorial, we examine the residuals for heteroscedasticity. If the OLS model is well-fitted there should be no observable pattern in the residuals. The residuals should show no perceivable relationship to the fitted values, the independent variables, or each other.