Database: student_club
Question: Calculate the difference in the percentage of members in New Jersey and Vermont.
SQL: SELECT CAST((SUM(CASE WHEN T2.state = 'New Jersey' THEN 1 ELSE 0 END) - SUM(CASE WHEN T2.state = 'Vermont' THEN 1 ELSE 0 END)) AS REAL) * 100 / COUNT(T1.member_id) AS diff FROM member AS T1 INNER JOIN zip_code AS T2 ON T2.zip_code = T1.zip