CakePHP 2.0 Retrieve Aggregate function inner Containable

$this->PollingText->Behaviors->load('Containable', array('autoFields' => false));
$pollings = $this->PollingText->find('all', array(
    'conditions' => array('PollingText.polling_category_id' => $category_id),
    'order' => array('PollingText.order_number' => 'ASC'),
    'contain' => array(
        'PollingQuestion',
    'PollingQuestion.PollingAnswer',
    'PollingQuestion.PollingAnswer.Respondent' => array(
        'conditions' => array(
            'Respondent.created BETWEEN ? AND ?' => array(
                $startDate->format('Y-m-d'),
            $endDate->format('Y-m-d')
                ),
            ),
        'group' => array('Respondent.created'),
            'fields' => array(
                'COUNT(Respondent.id) AS total_respondent',
                'Respondent.created'
            )
        ),
    ),
));