public function is_orphan( $deep = false ) {

		$parent_id = $this->get( 'lesson_id' );

		if ( ! $parent_id ) {
			return true;
		}

		/**
		 * This is to take into account possible data inconsistency.
		 *
		 * @link https://github.com/gocodebox/lifterlms/issues/1039
		 */
		if ( $deep ) {
			$lesson = llms_get_post( $parent_id );
			// Both the ids are already absint, see LLMS_Post_Model::___get().
			if ( ! $lesson || $this->get( 'id' ) !== $lesson->get( 'quiz' ) ) {
				return true;
			}
		}

		return false;
	}