def get_expr_for_filtering_allele_frequency(ac_field="va.AC[va.aIndex - 1]", an_field="va.AN", confidence_interval=0.95):
    """Compute the filtering allele frequency for the given AC, AN and confidence interval."""
    if not (0 < confidence_interval < 1):
        raise ValueError("Invalid confidence interval: %s. Confidence interval must be between 0 and 1." % confidence_interval)
    return "filtering_allele_frequency(%(ac_field)s, %(an_field)s, %(confidence_interval)s)" % locals()