# linearmodels.iv.results.IVResults.basmann¶

property IVResults.basmann: InvalidTestStatistic | WaldTestStatistic[source]

Basmann’s test of overidentifying restrictions

Returns:
WaldTestStatistic

Object containing test statistic, p-value, distribution and null

Notes

Requires more instruments than endogenous variables

Tests is a small-sample version of Sargan’s test that has the same distribution.

$s (n - n_{instr}) / (n - s) \sim \chi^2_{v}$

where $$n_{instr}$$ is the number of instruments, $$n_{exog}$$ is the number of exogenous regressors and $$n_{endog}$$ is the number of endogenous regressors. The degree of freedom is the difference between the number of instruments and the number of endogenous regressors.

$v = n_{instr} - n_{exog}$