The 2023 Kansas County Population Forecast is an Age-Cohort Survival Model, meaning the population present in the starting year is aged up through the model over time and is subject to mortality and fertility. However, people do not always live in one county, so migration into and out of counties is also considered. The model forecasts each 5-year age cohort from 0-4 years up to 85+ years of age every five years from 2026-2071, using Census American Community Survey (ACS) 5-year estimates from 2021 as the starting period.
Forecasts are produced simultaneously for persons' self-identified race and ethnicity: White alone, Black/African American alone, and Other (alone and multiple races). Total population estimates are the sum of White, Black/African American, and Other race. Hispanic is calculated separately and should not be added to the other races. Brief explanations of each of these primary forecast components are below.
Mortality – Using mortality rates from the Social Security Administration (https://www.ssa.gov/oact/STATS/table4c6.html) for males and females, persons in a 5-year age cohort are subjected to mortality before aging into the next 5-year age cohort in the following forecast year. Because SSA mortality rates are on a 1-year increment, we aggregate survival rates into an average mortality rate per 5-year age cohort. Rates differ between males and females, with female mortality tending to peak later than among males, leading to greater survivorship into late life.
Fertility – Using Kansas Information for Communities (KIC) and Missouri Public Health Information Management System (MOPHIMS) data from 2016 to 2020, the forecasts established fertility rates for a 5-year age cohort of females from 10-14 to 40-44 on a per-race/-ethnicity basis. Due to imprecise estimates of birth rates, particularly among minorities in low-minority-population counties, outliers are smoothed to the 40th(lower) and 60th(upper) percentile of the state average as an approximation. Instead of simply using flattened fertility rates by race, this calculation method allows the capture of unique county-specific phenomena that impact fertility. More detail on special considerations is detailed in Transitory Populations.
Migration – People do not always remain in their current county of residence. There are pre-existing trends of migration to and from counties. The model utilizes a CEDBR-produced long-term employment forecast by county as the basis for migration, including an average multiplier factor to capture families of workers who also migrate, though do not necessarily enter the labor force captured by employment; for example, children and persons engaged primarily in home-based childcare. Total migration estimates are allocated to each race/ethnicity using the share of in-migration represented by each group. The forecasts are further allocated to age groups, with the overwhelming majority of migration being persons of working age and their children.
Transitory Population – Some counties have distinct features and institutions that create unique concentrations of certain age groups with unique behaviors. Counties with public universities, military bases, and large community colleges or private universities tend to have outsized populations of persons in the 15-19 and 20-24 age cohorts. These populations are reflected in the ACS population estimates; however, they cannot be treated the same as the general population structure for the following reasons:
1: they are typically in-migrants from elsewhere,
2: upon completion of their education/term of military service, the majority out-migrate, and
3: these groups tend to have different rates of fertility
The model assumes that the transitory population does not contribute to fertility. To approximate this effect within the model, a certain quantity of 15-24-year-olds are in-migrated to these relevant counties. The sum of these in-migrants is "pulled" from the remainder of counties based on their respective share of the total state population. Upon completion of education/military service, assumed to be in the 25-34 age cohorts, 95% of the in-migrants return to their counties of origin, and the remaining 5% remain in the destination county to capture persons who settle/find employment. Certain counties like Sedgwick and Johnson differ slightly in retention rates and in-/out-migration.