def ses_ratio(self):
        """
        The ratio

        risk_investigation_time / investigation_time / ses_per_logic_tree_path
        """
        if self.investigation_time is None:
            raise ValueError('Missing investigation_time in the .ini file')
        return (self.risk_investigation_time or self.investigation_time) / (
            self.investigation_time * self.ses_per_logic_tree_path)