Dear Dr. Zahir, many thanks for your comment. There is unfortunately no better database available for data across countries, so we use the best available, the UN Population Division that uses country censuses to provide estimates on diaspora. We believe these are conservative numbers but comparable. In addition, countries do not have a common definition of diaspora. For example, Some include dual citizens while others don't. It is also hard to get an exact measurement of undeclared emigrants. The data is scattered between ministries and embassies. The World Bank is working with countries and partners to improve data collection on diaspora data worldwide, including in advanced economies.