user: Question: What is the reason for change when Maryland 6th is the district? 
Columns: ['District', 'Vacator', 'Reason for change', 'Successor', 'Date successor seated']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Kentucky 7th', 'George Robertson (DR)', 'resigned before Congress met', 'John S. Smith (DR)', 'Seated December 3, 1821']
SQL:

assistant: SELECT "Reason for change" FROM "Table" WHERE "District" = 'Maryland 6th';