'score first derivative of the loglikelihood for each observation.
Parameters
params : ndarray
parameter at which score is evaluated
scale : None or float
If scale is None, then the default scale will be calculated.
Default scale is defined by `self.scaletype` and set in fit.
If scale is not None, then it is used as a fixed scale.
Returns
score_obs : ndarray, 2d
The first derivative of the loglikelihood function evaluated at
params for each observation.'

def score_obs(self, params, scale=None):

    score_factor = self.score_factor(params, scale=scale)
    return (score_factor[:, None] * self.exog)
