protected function getAllowedPaymentFrequencies()
    {
        return array(
            static::DAILY,
            static::WEEKLY,
            static::SEMIMONTHLY,
            static::MONTHLY,
            static::BIMONTHLY,
            static::QUATERLY,
            static::EVERY_4_MONTHS,
            static::SEMIANNUAL,
            static::ANNUAL,
        );
    }