Table schema:
CREATE TABLE table_19948664_1 (countries_sampled INTEGER, ranking_la__2_ VARCHAR, author___editor___source VARCHAR, year_of_publication VARCHAR)

Question: How many countries were sampled in the index created by The Economist, published in 2007 and ranked 2nd in the LA Ranking?
SQL: SELECT MAX(countries_sampled) FROM table_19948664_1 WHERE author___editor___source = "The Economist" AND year_of_publication = "2007" AND ranking_la__2_ = "2nd"