The diversity in the level of economic development among the ASEAN countries is quite large. Singapore, the richest country in the group, has a per capita income close to 300 times the per capita income of Myanmar, the poorest country in the group. Even among the ASEAN–5 (Indonesia, Malaysia, Philippines, Singapore, and Thailand), the per capita income of Singapore is about 40 times the per capita income of Indonesia. This degree of diversity is higher than among the countries of the EU. It is sometimes argued that such a high degree of income differentials could make it difficult to sustain a monetary union among these countries. However, it is important to note that what is important for the adoption of a common currency among countries is that relative prices and outputs across them should have high co-movements following an economic shock, not so much that the levels of income should be more equal across them. For even if the countries in a monetary union have perfect equality of per capita incomes, if the co-movement of relative prices and outputs across countries is low, conducting a common monetary policy for the union as a whole is difficult.