Тяхната честота е определена въз основа на следната конвенция: чести (≥1/ 100 до < 1 / 10); нечести (≥1/ 1 000 до < 1/ 100); редки (≥1/ 10 000 до < 1/ 1 000); много редки (< 1/ 10 000).
Their frequency is defined using the following conventions: common (≥1/100 to < 1/10); uncommon (≥1/1,000 to < 1/100); rare (≥1/10,000 to < 1/1,000); very rare (< 1/10,000).