user: ### NOW ANSWER:
Question: What is the number of nurses in the region with an HO : Population Ratio of 1:16,791?
Columns: ['Region', 'Physician (GP & specialist)', 'Physician : Population Ratio', 'Health Officer', 'HO : Population Ratio', 'All Nurses', 'Nurse : Population Ratio', 'Mid-wives', 'Mid Wife: Population Ratio', 'HEW*']
Types: ['text', 'real', 'text', 'real', 'text', 'real', 'text', 'text', 'text', 'text']
Sample row: ['Tigray', 101.0, '1:44,880', 188.0, '1:24,111', 2332.0, '1:1,944', '185', '1:24,502', '1,433']
SQL:

assistant: SELECT AVG("All Nurses") FROM "Table" WHERE "HO : Population Ratio" = '1:16,791';