The actuarial sources of the rise in unfunded liabilities in America's defined benefit plans in the 21st century

Despite a decade-long bull market between the financial crisis and the COVID-19 recession, state defined benefit pension plans had accrued more than $1.37 trillion in unfunded liabilities. However, little work has investigated the actuarial sources of these unfunded liabilities. This paper uses original data hand collected from publicly available financial reports between 2000 and 2020 for 145 state-administered pension plans to determine the sources of unfunded liabilities. The largest unfunded liability contributor is investment experiences (when actual investment returns do not match assumed returns). The second and third largest contributors are changes to actuarial assumptions and expected changes (or interest accruing on existing unfunded liabilities). Benefit experience and legislative changes, demographic experience, and explicit funding shortfalls account for relatively little of the growth in unfunded liabilities. Moreover, the specific sources of unfunded liabilities are heterogeneous over time and across plans.