Contents
What is the null hypothesis of heteroscedasticity?
A graph showing heteroscedasticity; the White test is used to identify heteroscedastic errors in regression analysis. The null hypothesis for White’s test is that the variances for the errors are equal. In math terms, that’s: H0 = σ2i = σ2.
What is perfect Multicollinearity?
Perfect multicollinearity is the violation of Assumption 6 (no explanatory variable is a perfect linear function of any other explanatory variables). Perfect (or Exact) Multicollinearity. If two or more independent variables have an exact linear relationship between them then we have perfect multicollinearity.
Why is heteroscedasticity bad?
What Problems Does Heteroscedasticity Cause? Heteroscedasticity tends to produce p-values that are smaller than they should be. This effect occurs because heteroscedasticity increases the variance of the coefficient estimates but the OLS procedure does not detect this increase.
How does the Breusch-Pagan test check for heteroscedasticity?
The Breusch-Pagan test only checks for the linear form of heteroskedasticity i.e. it models the error variance as σ i 2 = σ 2 h ( z i ′ α) where z i is a vector of your independent variables. It tests H 0: α = 0 versus H a: α ≠ 0.
How is the null hypothesis tested in Breusch Pagan?
Breusch-Pagan / Cook-Weisberg tests the null hypothesis that the error variances are all equal versus the alternative that the error variances are a multiplicative function of one or more variables. For example, in the default form of the hettest command shown above,…
When did Trevor Breusch and Adrian Pagan create the test?
In statistics, the Breusch–Pagan test, developed in 1979 by Trevor Breusch and Adrian Pagan, is used to test for heteroskedasticity in a linear regression model. It was independently suggested with some extension by R. Dennis Cook and Sanford Weisberg in 1983 ( Cook–Weisberg test ).
How to do the Breusch Pagan test in Python?
In Python, there is a method het_breuschpagan in statsmodels.stats.diagnostic (the statsmodels package) for Breusch–Pagan test. In gretl, the command modtest –breusch-pagan can be applied following an OLS regression.