public function getRespondent($patientId, $organizationId, $respondentId = null)
    {
        if ($patientId) {
            if (isset($this->_respondents[$organizationId][$patientId])) {
                return $this->_respondents[$organizationId][$patientId];
            }
        }
        $newResp = $this->_loadClass('Tracker_Respondent', true, array($patientId, $organizationId, $respondentId));
        $patientId = $newResp->getPatientNumber();

        if (! isset($this->_respondents[$organizationId][$patientId])) {
            $this->_respondents[$organizationId][$patientId] = $newResp;
        }

        return $this->_respondents[$organizationId][$patientId];
    }