CREATE TABLE table_name_16 (points INTEGER, year VARCHAR(255), entrant VARCHAR(255), chassis VARCHAR(255))
What are the average points of Scuderia Scribante with a Brabham bt11 chassis before 1968?
    
SQL: SELECT AVG(points) FROM table_name_16 WHERE entrant = "scuderia scribante" AND chassis = "brabham bt11" AND year < 1968