Question: how many of the parties are popular? | What do you mean by popular? | how many parties have the most popular party form?
SQL: SELECT count ( * )  FROM parties AS t1 JOIN party_forms AS t2 ON t1.party_id   =   t2.party_id WHERE t2.form_id   =    ( SELECT form_id FROM party_forms GROUP BY form_id ORDER BY count ( * )  DESC LIMIT 1 )