Intercensal Estimates of the Resident Population. At the national level, the resident population is affected by births, deaths, and net international migration (NIM) only. Pop. Estimate = Base Pop+BerthsDeaths+NIM At the sub-national level (i.e., states and counties), the resident population is affected by an additional component of population change: net internal, or domestic, migration (NDM). Pop. Estimate = Base Pop+BerthsDeaths+NIM+NDM.