On comparing cost of living of cities using expatriate price survey

Commercial cost of living indexes, which are nominal Laspeyres price indexes derived from expatriate price surveys, are increasingly used in policy debate. However, these indexes contain two systematic errors – (1) using nominal exchange rate, instead of the purchasing power parity equivalent, cause upward biases in high income cities and (2) using a fixed basket causes upward biases in cities with different consumption pattern – that make them unfit for the purpose of policy debate if the errors are serious enough. Using a real Fisher index corrects these systemic errors. We showed high congruence in pair-wise comparison between these two indexes, but substantial differences in ranking arising from the systematic errors. Commercial indexes are useful for designing expatriate compensation, but we need a real Fisher index to calculate and rank the cost of living among cities.