public function createList($title, $unsubscribePage = null, $confirmOptIn = false, $confirmationSuccessPage = null, $clientId = null)
{
// set client ID
$clientId = empty($clientId) ? $this->getClientId() : $clientId;
// set parameters
$parameters['Title'] = (string) $title;
$parameters['UnsubscribePage'] = (string) $unsubscribePage;
$parameters['ConfirmedOptIn'] = $confirmOptIn ? true : false;
$parameters['ConfirmationSuccessPage'] = (string) $confirmationSuccessPage;
// return the result
return (string) $this->doCall('lists/' . $clientId, $parameters, 'POST');
}