@property<EOL><INDENT>@cache<EOL>def null_beta_covariance(self):<DEDENT>
return self.null_scale * pinv(self._H)<EOL>
Covariance of the optimal 𝛃 according to the marginal likelihood.

Returns
-------
effsizes-covariance : ndarray
    s(MᵀK⁻¹M)⁻¹.