user: Question: Of all the schools that left before 2003, what is the average year joined?
Columns: ['School', 'Location', 'Mascot', 'County', 'Year Joined', 'Previous Conference', 'Year Left', 'Conference Joined']
Types: ['text', 'text', 'text', 'text', 'real', 'text', 'real', 'text']
Sample row: ['Argos', 'Argos, IN', 'Dragons', '50 Marshall', 1998.0, 'independent', 2008.0, 'independent']
SQL:

assistant: SELECT AVG("Year Joined") FROM "Table" WHERE "Year Left" < 2003.0;