Честотата се дефинира както следва: много чести: ≥ 1/ 10, чести: ≥ 1/ 100 и < 1/ 10, нечести: ≥ 1/ 1 000 и < 1/ 100, редки: ≥ 1/ 10 000 и < 1/ 1 000, много редки: ≤ 1/ 10 000.
The frequency is defined as follows: very common: ≥ 1/ 10, common: ≥ 1/ 100 and < 1/ 10, uncommon: ≥ 1/ 1,000 and < 1/ 100, rare: ≥ 1/ 10,000 and < 1/ 1,000, very rare: ≤ 1/ 10,000.