'Evaluates the fitted emirical null Z-score density.
Parameters
zscores : scalar or array-like
The point or points at which the density is to be
evaluated.
Returns
The empirical null Z-score density evaluated at the given
points.'

def pdf(self, zscores):

    zval = ((zscores - self.mean) / self.sd)
    return np.exp(((((-0.5) * (zval ** 2)) - np.log(self.sd)) - (0.5 * np.log((2 * np.pi)))))
