A simple growth model of open economies
修改索洛模型的储蓄假设，使储蓄来自资本收入而非总收入，从而让模型同时适用于封闭和开放经济，并解释国家间财富与收入的长期差异。
Abstract This paper makes a small twist to a seemingly simple assumption in the Solow model: instead of agents saving a fraction of their entire income, as in the classic Solow model, they here save a fraction of their capital income. This twist makes the Solow model fit the main properties of the Ramsey–Cass–Koopmans model, not only for closed economies but also for open economies. Its tractability enables closed‐form characterization of the convergence properties of an arbitrary number of countries, with arbitrary population sizes and with initially different levels of capital. It makes explicit that initial differences in capital intensity between countries implies long‐run differences in wealth, and thus also in income because the initially rich countries will own part of the capital placed in poorer countries. In line with empirical observations, it predicts that: income growth will be U‐shaped in initial income; rich countries will save more of their income; and poor countries will see growth mainly in their labor income.