Write SQL query to solve given problem: What is the difference of female and male audiences in number who viewed horror movies?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(IIF(T2.u_gender = 'F', 1, 0)) - SUM(IIF(T2.u_gender = 'M', 1, 0)) FROM u2base AS T1 INNER JOIN users AS T2 ON T1.userid = T2.userid INNER JOIN movies2directors AS T3 ON T3.movieid = T1.movieid WHERE T3.genre = 'horror'