По честота се определят като много чести (≥1/ 10); чести (≥1/ 100, < 1/ 10); нечести (≥1/ 1 000, < 1/ 100); редки (≥1/ 10 000, < 1/ 1 000) и много редки (< 1/ 10 000).
Frequencies are defined as: very common (≥ 1/ 10), common (≥ 1/ 100, < 1/ 10), uncommon (≥ 1/ 1000, < 1/ 100), rare (≥ 1/ 10,000, < 1/ 1000) and very rare (< 1/ 10,000).