def calculate_RR_for_motif(ct):
    """
    Motif is treatment
    No motif is placebo

    :param ct: mutually exclusive counts of mutated matching motifs, matching mutations, matching motifs, and matching bases
    :return: enrichment or risk ratio
    """
    try:
        RR = ((ct.loc['mutation', 'motif'] / (ct.loc['mutation', 'motif'] + ct.loc['no mutation', 'motif'])) /
              (ct.loc['mutation', 'no motif'] / (ct.loc['mutation', 'no motif'] + ct.loc['no mutation', 'no motif'])))
    except ZeroDivisionError:
        RR = 0.0
    return RR