Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_19948664_2 (index__year_ VARCHAR, countries_sampled VARCHAR)
### Question:
How many years were listed under index when there were 157 countries sampled?
### Answer:
SELECT COUNT(index__year_) FROM table_19948664_2 WHERE countries_sampled = 157