CREATE TABLE table_23449 ("Index  ( Year ) " TEXT, "Author / Editor / Source" TEXT, "Year of publication" TEXT, "Countries sampled" FLOAT, "World Ranking  ( 1 ) " TEXT, "Ranking L.A.  ( 2 ) " TEXT)

How many years were recorded when world ranking was 21st?
SELECT COUNT("Index (Year)") FROM table_23449 WHERE "World Ranking (1)" = '21st'
SELECT COUNT("Index (Year)") FROM "table_23449" WHERE "World Ranking (1)" = '21st'