user: Question: How many countries were sampled for the Prosperity Index (2008)?
Columns: ['Index (Year)', 'Author / Editor / Source', 'Year of publication', 'Countries sampled', 'World Ranking (1)', 'Ranking L.A. (2)']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Human Poverty, HPI-1 (2005) (3)', 'United Nations (UNDP)', '2007–08', 108.0, '2nd', '1st']
SQL:

assistant: SELECT "Countries sampled" FROM "Table" WHERE "Index (Year)" = 'Prosperity Index (2008)';