@property<EOL><INDENT>def beta(self):<DEDENT>
from numpy_sugar.linalg import rsolve<EOL>return rsolve(self._X["<STR_LIT>"], rsolve(self._X["<STR_LIT>"], self.mean()))<EOL>
Fixed-effect sizes.

Returns
-------
effect-sizes : numpy.ndarray
    Optimal fixed-effect sizes.

Notes
-----
Setting the derivative of log(p(𝐲)) over effect sizes equal
to zero leads to solutions 𝜷 from equation ::

    (QᵀX)ᵀD⁻¹(QᵀX)𝜷 = (QᵀX)ᵀD⁻¹(Qᵀ𝐲).