CREATE TABLE table_18591 ("District" CLOB, "Incumbent" CLOB, "Party" CLOB, "First elected" FLOAT, "Result" CLOB, "Candidates" CLOB)

How many districts have an incumbent first elected in 1940?
SELECT COUNT("District") FROM table_18591 WHERE "First elected" = '1940'
SELECT COUNT("District") FROM "table_18591" WHERE "First elected" = '1940'