def _calculate_compliance(results):
    """
    Calculate compliance numbers given the results of audits
    """
    success = len(results.get('Success', []))
    failure = len(results.get('Failure', []))
    control = len(results.get('Controlled', []))
    total_audits = success + failure + control

    if total_audits:
        compliance = float(success + control) / total_audits
        compliance = int(compliance * 100)
        compliance = '{0}%'.format(compliance)
        return compliance
    return None