Explanation:

- Option 1: Agriculture based population

- This option refers to the number of people involved in agriculture. It's not related to the headcount ratio.

- Option 2: Literacy rate

- The literacy rate measures the percentage of literate individuals in a population. Headcount ratio is unrelated to literacy metrics.

- Option 3: International Migration

- This measures movement across countries. Headcount ratio does not measure migration statistics.

- Option 4: Poverty

- The headcount ratio measures poverty. It reflects the share of a population living below the poverty line.

. The headcount ratio indeed measures poverty.