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| Homoskedasticity means that the variance of the error term is constant and not correlated to any treatment or control variable. | Mathematically, homoskedasticity and [[Econometrics/Exogeneity|exogeneity]] together can be expressed as: {{attachment:exo.svg}} The full set of variables is independently and normally distributed about 0. The covariance matrix is fully expressed as the [[LinearAlgebra/SpecialMatrices#Diagonal_Matrices|diagonal matrix]] of each term's variance. |
Homoskedasticity
Homoskedasticity means that the variance of the error term is constant and not correlated to any treatment or control variable.
Contents
Meaning
Mathematically, homoskedasticity and exogeneity together can be expressed as:
The full set of variables is independently and normally distributed about 0. The covariance matrix is fully expressed as the diagonal matrix of each term's variance.
The opposite condition is heteroscedasticity.
It can also be useful to express exogeneity as a conditional expectation like:
