⁷The word is in quotes because we refer here not to the pure time preference rate but instead to a relation between time preference rate, the interest rate, relative risk aversion, the intertemporal elasticity of substitution, the magnitude of risk, and expected income growth. All of these surely vary in the population, but we argue that few if any important macroeconomic questions depend on which particular kinds of heterogeneity are most responsible for the heterogeneity in wealth-to-income ratios. See subsection 2.4 for a fuller discussion.