def _analyze_root_causes(self):
        """
        Conduct root cause analysis.
        The first metric of the list is taken as the root cause right now.
        """
        causes = {}
        for a in self.anomalies:
            try:
                causes[a] = self.correlations[a][0]
            except IndexError:
                raise exceptions.InvalidDataFormat('luminol.luminol: dict correlations contains empty list.')
        self.causes = causes