• Very common: affects more than 1 user in 10 • Common: affects 1 to 10 users in 100 • Uncommon: affects 1 to 10 users in 1,000 • Rare: affects 1 to 10 users in 10,000 • Very rare: affects less than 1 user in 10,000 • Not known: frequency cannot be estimated from the available data