CREATE TABLE table_18373 ("District" TEXT, "Incumbent" TEXT, "Party" TEXT, "First elected" FLOAT, "Result" TEXT, "Candidates" TEXT)

what is the party when the incumbent is sidney r. yates?
SELECT "Party" FROM table_18373 WHERE "Incumbent" = 'Sidney R. Yates'
SELECT "Party" FROM "table_18373" WHERE "Incumbent" = 'Sidney R. Yates'