def insert_ethinca_metric_options(parser):
    """
    Adds the options used to calculate the ethinca metric, if required.
 
    Parameters
    -----------
    parser : object
        OptionParser instance.
    """
    ethincaGroup = parser.add_argument_group("Ethinca metric options",
                    "Options used in the calculation of Gamma metric "
                    "components for the ethinca coincidence test and for "
                    "assigning high-frequency cutoffs to templates.")
    ethinca_methods = ethincaGroup.add_mutually_exclusive_group()
    ethinca_methods.add_argument("--calculate-time-metric-components",
                    action="store_true", default=False,
                    help="If given, the ethinca metric will be calculated "
                    "for only the time component, and stored in the Gamma0 "
                    "entry of the sngl_inspiral table. OPTIONAL, default=False")
    ethinca_methods.add_argument("--calculate-ethinca-metric",
                    action="store_true", default=False, 
                    help="If given, the ethinca metric will be calculated "
                    "and stored in the Gamma entries of the sngl_inspiral "
                    "table. OPTIONAL, default=False")
    ethincaGroup.add_argument("--ethinca-pn-order",
                    default=None, choices=get_ethinca_orders(), 
                    help="Specify a PN order to be used in calculating the "
                    "ethinca metric. OPTIONAL: if not specified, the same "
                    "order will be used as for the bank metric.")
    ethincaGroup.add_argument("--filter-cutoff",
                    default=None, 
                    choices=pnutils.named_frequency_cutoffs.keys(),
                    help="Specify an upper frequency cutoff formula for the "
                    "ethinca metric calculation, and for the values of f_final"
                    " assigned to the templates.  REQUIRED if the "
                    "calculate-ethinca-metric option is given.")
    ethincaGroup.add_argument("--ethinca-frequency-step", action="store",
                    type=float, default=10.,
                    help="Control the precision of the upper frequency cutoff."
                    " For speed, the metric is calculated only for discrete "
                    "f_max values with a spacing given by this option. Each "
                    "template is assigned the metric for the f_max closest to "
                    "its analytical cutoff formula. OPTIONAL, default=10. "
                    "UNITS=Hz")

    return ethincaGroup
Adds the options used to calculate the ethinca metric, if required.
 
    Parameters
    -----------
    parser : object
        OptionParser instance.