# spreg.white¶

spreg.white(reg)[source]

Calculates the White test to check for heteroscedasticity. [Whi80]

Parameters
regregression object

output instance from a regression model

Returns
white_resultdictionary

contains the statistic (white), degrees of freedom (df) and the associated p-value (pvalue) for the White test.

whitefloat

scalar value for the White test statistic.

dfinteger

degrees of freedom associated with the test

pvaluefloat

p-value associated with the statistic (chi^2 distributed with k df)

Notes

x attribute in the reg object must have a constant term included. This is standard for spreg.OLS so no testing done to confirm constant.

Examples

>>> import numpy as np
>>> import libpysal
>>> from libpysal import examples
>>> import spreg
>>> from spreg import OLS


Read the DBF associated with the Columbus data.

>>> db = libpysal.io.open(examples.get_path("columbus.dbf"),"r")


Create the dependent variable vector.

>>> y = np.array(db.by_col("CRIME"))
>>> y = np.reshape(y, (49,1))


Create the matrix of independent variables.

>>> X = []
>>> X.append(db.by_col("INC"))
>>> X.append(db.by_col("HOVAL"))
>>> X = np.array(X).T


Run an OLS regression.

>>> reg = OLS(y,X)


Calculate the White test for heteroscedasticity.

>>> testresult = spreg.white(reg)


Print the degrees of freedom for the test.

>>> print(testresult['df'])
5


Print the test statistic.

>>> print("%1.3f"%testresult['wh'])
19.946


Print the associated p-value.

>>> print("%1.4f"%testresult['pvalue'])
0.0013