JEL Classification：F19 N15 O53

1 Introduction

The International Comparison Program （ICP） is a worldwide statistical operation，which computes the trust worthiest Purchasing Power Parities （PPPs） at country and international level，taking into account the methodological and practical problems of the computation. The 2011 Round involved nearly 200 countries.

The PPPs deal with the comparisons of price levels across different countries or areas. They are useful for a wide variety of purposes，because using PPPs instead of market exchange rates to convert currencies makes it possible to compare the Gross Domestic Product （GDP） and/or its components and the welfare，poverty and living conditions of the inhabitants of different countries in real terms （that is，controlling the differences in price levels）.

However，when in 2014 the World Bank published the 2011 ICP Round PPPs data，showing changes to relative income levels that were larger in lower-income countries，thereby narrowing the world income distribution，several users （researchers，policy makers，economic operators，journalist，etc.） did not accept the results as valid （see the ICP web site：ICP 2011 Media & Blog Coverage）. This has attracted a good deal of attention，particularly on the fact that the aggregate Chinese economy and the US economy seem much closer than previously estimated，and also that the Indian economy is larger than the Japanese economy. During the debates，many media in China highlighted the fact that National Bureau of Statistics of China did not recognize the PPPs as official statistics^[1].

Particularly，the data users seem not to justify both the differences in the average prices level of two countries and the differences from the results of ICP 2005