Joe's Blog

Census Data vs. Disaster Reality

We've been working on projects in areas that have suffered weather related disasters. Within those projects we have to compare housing lost and population displaced with current census projections. Have you ever wondered how the United States Census Bureau formulates their projected population figures? And, do they allot for potential natural disasters? We're here to shed some light on the subject.

The US Census Bureau typically develops their population projections (estimates) starting with the most recent decennial census then applying the "cohort-component method." These projections take into account possible changes based on assumptions on future births, deaths, and international and domestic migration.

Using the cohort-component method, updated numbers in a census group are generated by applying specified mortality and migration assumptions to that group. For example, specified fertility assumptions are applied to the female population of childbearing age to derive new birth cohorts.

According to the US Census Bureau, some events such as the natural disasters that occurred in Tuscaloosa, Ala., and Joplin, Mo., in 2011 are unpredictable. Their impact on a population cannot be foreseen and are not taken into consideration when projecting population figures.

By Rachel Ballard