What is the ratio between male and female legislators?
ratio = DIVIDE(SUM(gender_bio = 'M'),  SUM(gender_bio = 'F')); male refers to gender_bio = 'M'; female refers to gender_bio = 'F'
SELECT CAST(SUM(CASE WHEN gender_bio = 'M' THEN 1 ELSE 0 END) AS REAL) / SUM(CASE WHEN gender_bio = 'F' THEN 1 ELSE 0 END) FROM historical