The parameters p and o are, as observed earlier, not separately identified, but if their joint values differed over countries in such a way as to account for income differences, poor countries would have systematically much higher (risk-corrected) interest rates than rich countries. Even if this were true, I would be inclined to seek other explanations. Looking ahead, we would like also to be able to account for sudden large changes in growth rates of individual countries. Do we want a theory that focuses attention on spontaneous shifts in people's discount rates or degree of risk aversion? Such theories are hard to refute, but I will leave it to others to work this side of the street.