Net migration (in thousand) for the specific five-year time period (i.e., from 1 July in year t to 1 July in year t+5 such as the period 1950-1955 refers to the period 1950.5-1955.5 and the mid of the period is 1953.0).
Source
These datasets are based on estimates and projections of United Nations, Department of Economic and Social Affairs, Population Division (2015).