The highest dan ranks are sometimes reserved for the founder or leaders of a style and only high-ranking students can be promoted to them. For example, only five living people hold a tenth dan in judo and only about thirty-five worldwide have been promoted to the rank since its inception; of those 10th dan promotions only fifteen were conferred by the Kodokan, all of them to Japanese judoka. This has led to upper level ranks becoming extinct in some arts. In other styles, the dan ranks are not the highest level that might be attained, with instructor certification and judge/judgment authorization being understood as higher-level or more sophisticated.