Determines the "scores" of the cluster, the metric that determines the
        size of the cluster visualized on the visualization.

def _score_clusters(self, X, y=None):
        """
        Determines the "scores" of the cluster, the metric that determines the
        size of the cluster visualized on the visualization.
        """
        stype = self.scoring.lower() # scoring method name

        if stype == "membership":
            return np.bincount(self.estimator.labels_)

        raise YellowbrickValueError("unknown scoring method '{}'".format(stype))