Source: Authors' calculations based on PovcalNet database. Haughton and Khandker (2010) go as far as stating that "legitimate comparisons of poverty rates between one country and another can only be made if the same absolute poverty line is used in both countries". The statement that the same line should be used depends crucially on the validity and legitimacy of that poverty line in both countries, which is likely to hold when both are low-income countries -because below a certain level of income, poverty lines are quite close to the dollar-a-day line—but not among two middle-income countries.