The comparison of poverty rates across two countries, or across regions within a country, is a common occurrence in analysis produced at the World Bank and other development agencies, as well as in published academic papers. For any poverty comparison to have meaning, however, the analyst needs to norm the various observed states of the world to a known standard of living.
John Gibson and Trinh Le's study found local expert opinion on prices is a good substitute for (and cheaper than) a full-fledged market price survey.
You can read the World Bank blog on this paper or the paper itself.
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