Social scientists and policy makers often lament the quality of data on international migration. Besides the lack of robust and comparable data, the field of international migration is beset with conflicting concepts, definitions and often, misleading terminology. This paper attempts a comprehensive stocktaking of international migration data. The focus is on international and long-term migration to purpose the data for international migration projections. It is a broad review of data sources, distinguishing between migration flow statistics and statistics on migrant stocks (migrant or immigrant populations). An overview of estimates on net migration has also been incorporated in this paper.

Migrant flows and migrant stock data originate from two different sources: the first is primary data collection by National Statistical Offices (NSO), and the second is data from subsequent efforts to either improve coverage, compatibility and consistency of raw data or, from efforts to generate estimates by transforming stock data into flow data. The stocktaking exercise confirms the severe lack of timely, consistent and comparable migration data. The paper, thus calls to follow a multipronged approach in future data collection endeavors, with better collaboration between official statistics and model-based estimation and projections.