1. For 1 dollar you can buy more in one country than in another. That is why purchasing power parity was coined → converted number of goods or services in a country for 1 dollar.
2. Informal sector does not count for the economy, in poor countries it is larger than the formal sector.
3. The GNP is an average, deviations from it can be very large. There may be social inequality, the biggest differences are in the semi-periphery group.
4. The GNP does not show regional differences, there may be regional inequality.