'Anscombe residuals for the Poisson distribution
Parameters
endog : array-like
Endogenous response variable
mu : array-like
Fitted mean response variable
scale : float, optional
An optional argument to divide the residuals by sqrt(scale).
The default is 1.
Returns
resid_anscombe : array
The Anscome residuals for the Poisson family defined below
Notes
.. math::
resid\_anscombe_i = (3/2) * (Y_i^{2/3} - \mu_i^{2/3}) / \mu_i^{1/6}'

def resid_anscombe(self, endog, mu, scale=1.0):

    return (((3 / 2.0) * ((endog ** (2 / 3.0)) - (mu ** (2 / 3.0)))) / ((mu ** (1 / 6.0)) * (scale ** 0.5)))
