Calculate the 2016 gap between the average revenue for Indian and American films.
2016 refers to release_date LIKE '2016%'; Indian and American films refers to country_name = 'India' and country_name = 'United States of America'; gap between the average revenue refers to subtract(divide(sum(revenue), count(movie_id)) when country_name = 'United States of America', divide(sum(revenue), count(movie_id)) when country_name = 'India')
SELECT AVG(CASE WHEN T3.COUNTry_name = 'United States of America' THEN T1.revenue END) - AVG(CASE WHEN T3.COUNTry_name = 'India' THEN T1.revenue END) AS CALCULATE FROM movie AS T1 INNER JOIN production_COUNTry AS T2 ON T1.movie_id = T2.movie_id INNER JOIN COUNTry AS T3 ON T2.COUNTry_id = T3.COUNTry_id WHERE CAST(STRFTIME('%Y', T1.release_date) AS INT) = 2016