What is the percentage of severe cases that are related to sexual assault?
related to sexual assault refers to primary_description = 'CRIME SEXUAL ASSAULT'; severe case refers to index_code = 'I'; percentage = Divide (Count (iucr_no where primary_description = 'CRIME SEXUAL ASSAULT'), Count (iucr_no)) * 100
SELECT CAST(SUM(CASE WHEN primary_description = 'CRIM SEXUAL ASSAULT' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) FROM IUCR WHERE index_code = 'I'