public function remove_form_stats($form_id)
 {
     if (is_array($form_id)) {
         foreach ($form_id as $formId) {
             RM_DBManager::delete_form_stats($formId);
         }
     } elseif ((int) $form_id) {
         RM_DBManager::delete_form_stats($form_id);
     } else {
         throw new InvalidArgumentException("Invalid Form ID '{$form_id}'.");
     }
 }