Financial Market Assumptions & Models for Pension Plans: A Technical Comment on the PIMS Model Assumptions for Asset Markets

The financial market assumptions of the PBGC’s PIMS model are critical inputs to simulations for most apparent uses of the system. They currently appear to be based on a reduced form, “classical” approach to assessing and forecasting the distribution of returns on various classes of input assets, allowing for a fairly sophisticated and useful approach to understanding simulated distributions of potential pension insurance outcomes as well as the net financial status of the PBGC. This technical note discusses some of the capital market side assumptions utilized in the model. It also comments on important related assumptions including the assumed asset allocations of insured plans, making suggestion for possible modification of input assumptions of the model to reflect time variation in financial market return behavior as well as time variation in observed plan allocations.