def _lnqmed_residual(catchment):
        """
        Return ln(QMED) model error at a gauged catchment

        :param catchment: Gauged catchment
        :type catchment: :class:`Catchment`
        :return: Model error
        :rtype: float
        """
        analysis = QmedAnalysis(catchment, year=2000)  # Probably should set the year to the midpoint of amax rec.
        logmedian_amax = log(analysis.qmed(method='amax_records'))
        logmedian_descr = log(analysis.qmed(method='descriptors'))
        return logmedian_amax - logmedian_descr