Kohortlivstabeller

kohortlivstabeller, or cohort life tables, are statistical tools used in demography to summarize the survival and mortality experience of a defined birth cohort as it ages. Unlike period life tables, which apply mortality rates from a single calendar year to a hypothetical cohort, kohortlivstabeller reflect the actual experience of people born in the same year as they progress through age. They provide a longitudinal view of mortality and are commonly used to estimate life expectancy and survival patterns for specific cohorts.

Construction typically proceeds from a starting number alive at birth, l0, and records the number of deaths and survivors in each age interval. Key quantities include l_x (number alive at the start of age x), d_x (deaths during the interval), q_x (probability of dying in the interval), and e_x (life expectancy at age x). In a true kohortlivstabel, l_x is built by chaining observed survival from age 0 onward for the cohort in question.

Data sources include national civil registries, vital statistics, and longitudinal studies that track individuals over many years. The approach requires long follow-up and complete registration of deaths; incomplete data are addressed by censoring methods and statistical adjustments. In modern practice, kohortlivstabeller may blend observed data with projections for ages beyond the last observed, and sometimes incorporate corrections for delays in reporting.

Uses and limitations: kohortlivstabeller are central to demographic research, actuarial practice, and policy analysis, providing estimates of cohort life expectancy and changes in mortality over time. They capture cohort-specific mortality improvements but depend on data quality and the duration of follow-up; for younger cohorts, the full lifetime experience may be unavailable, necessitating projection or hybrid methods. They complement period life tables by highlighting historical trends in survival for particular birth cohorts.