How many years were listed under index when there were 157 countries sampled?
CREATE TABLE table_19948664_2 (
    index__year_ VARCHAR,
    countries_sampled VARCHAR
)
SELECT COUNT(index__year_) FROM table_19948664_2 WHERE countries_sampled = 157
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: How many years were listed under index when there were 157 countries sampled? ### Input: CREATE TABLE table_19948664_2 (
    index__year_ VARCHAR,
    countries_sampled VARCHAR
) ### Response: SELECT COUNT(index__year_) FROM table_19948664_2 WHERE countries_sampled = 157