def get_truth_cand_ratio(t_err_cand, dm_err_cand, t_err_truth, dm_err_truth):
    """ Calculate ratio of truth region to candidate region, 
    to test upper limit of False Positives 
    """
    area_cand = t_err_cand*dm_err_cand
    area_truth = t_err_truth*dm_err_truth

    return area_truth/area_cand