CREATE TABLE table_64112 ("Date Released" CLOB, "Polling institute" CLOB, "Socialist" CLOB, "Social Democratic" CLOB, "Green-Communist" CLOB, "People's Party" CLOB, "Left Bloc" CLOB, "Lead" CLOB)

Which polling institute has a 30.7% for social democratic?
SELECT "Polling institute" FROM table_64112 WHERE "Social Democratic" = '30.7%'
SELECT "Polling institute" FROM "table_64112" WHERE "Social Democratic" = '30.7%'