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Overlapping Generations Models of the Economy

By John Geanakoplos - Yale
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Lecture Description

In order for Social Security to work, people have to believe there's some possibility that the world will last forever, so that each old generation will have a young generation to support it. The overlapping generations model, invented by Allais and Samuelson but here augmented with land, represents such a situation. Financial equilibrium can again be reduced to general equilibrium. At first glance it would seem that the model requires a solution of an infinite number of supply equals demand equations, one for each time period. But by assuming stationarity, the whole analysis can be reduced to one equation. In this mathematical framework we reach an even more precise and subtle understanding of Social Security and the real rate of interest. We find that Social Security likely increases the real rate of interest. The presence of land, an infinitely lived asset that pays a perpetual dividend, forces the real rate of interest to be positive, exposing the flaw in Samuelson's contention that Social Security is a giant, yet beneficial, Ponzi scheme where each generation can win by perpetually deferring a growing cost.

Course Description

Course Index

  1. Why Finance?
  2. Utilities, Endowments, and Equilibrium
  3. Computing Equilibrium
  4. Efficiency, Assets, and Time
  5. Present Value Prices and the Real Rate of Interest
  6. Irving Fisher's Impatience Theory of Interest
  7. Collateral, Present Value and the Vocabulary of Finance
  8. Budgeting for a Long-Lived Institution, Yield
  9. Dynamic Present Value
  10. Social Security
  11. Overlapping Generations Models of the Economy
  12. Demography and Asset Pricing
  13. Quantifying Uncertainty and Risk
  14. Uncertainty and the Rational Expectations Hypothesis
  15. Backward Induction and Optimal Stopping Times
  16. Callable Bonds and the Mortgage Prepayment Option
  17. Modeling Mortgage Prepayments and Valuing Mortgages
  18. History of the Mortgage Market: A Personal Narrative
  19. Dynamic Hedging
  20. Dynamic Hedging and Average Life
  21. Risk Aversion and the Capital Asset Pricing Theorem
  22. The Mutual Fund Theorem and Covariance Pricing Theorems
  23. Risk, Return, and Social Security
  24. The Leverage Cycle and the Subprime Mortgage Crisis
  25. The Leverage Cycle and Crashes