There is a joke about a professor who says "it is obvious that..." is interrupted by a student who asks "But is it really obvious?..." and then covers the blackboard with equations for thirty minutes in silence before finally announcing "Yes, it is obvious."
That's what I feel like with the claim that Dean Baker, Paul Krugman, and I made in our "Asset Returns and Economic Growth" that higher rates of return on assets made one look more favorably on prefunding and that higher rates of economic growth made one look more favorably on pay-as-you-go systems. I thought it was obvious. But it seemed that my intuition was not general.
Here's a sketch of the argument:
J. Bradford DeLong (2005), "A Note on Returns, Growth, and the Funding of Social Insurance" (Berkeley: U.C. Berkeley).