I follow R. A. Fisher's The Design of Experiments (1935), using randomization statistical inference to test the null hypothesis of no treatment effects in a comprehensive sample of 53 experimental papers drawn from the journals of the American Economic Association. In the average paper, randomization tests of the significance of individual treatment effects find 13% to 22% fewer significant results than are found using authors’ methods. In joint tests of multiple treatment effects appearing together in tables, randomization tests yield 33% to 49% fewer statistically significant results than conventional tests. Bootstrap and jackknife methods support and confirm the randomization results.

Using population and product consumption data from the Demographic and Health Surveys, I construct comparable measures of inequality and migration for 65 countries, including some of the poorest countries in the world. I find that the urban-rural gap accounts for 40% of mean country inequality and much of its cross-country variation. One out of every four or five individuals raised in rural areas moves to urban areas as a young adult, where they earn much higher incomes than nonmigrant rural permanent residents. Equally, one out of every four or five individuals raised in urban areas moves to rural areas as a young adult, where they earn much lower incomes than their nonmigrant urban cousins. These flows and relative incomes are suggestive of a world where the population sorts itself geographically on the basis of its human capital and skill. I show that a simple model of this sort explains the urban-rural gap in living standards.

This paper simulates the impact of the AIDS epidemic on future living standards in South Africa.I emphasize two competing effects.On the one hand, the epidemic is likely to have a detrimental impact on the human capital accumulation of orphaned children.On the other hand, widespread community infection lowers fertility, both directly, through a reduction in the willingness to engage in unprotected sexual activity, and indirectly, by increasing the scarcity of labour and the value of a woman's time.I find that even with the most pessimistic assumptions concerning reductions in educational attainment, the fertility effect dominates.The AIDS epidemic, on net, enhances the future per capita consumption possibilities of the South African economy.

Using an endogenous growth model in which learning by doing, although bounded in each good, exhibits spillovers across goods, this paper investigates the dynamic effects of international trade. Examining an LDC and a DC, the latter distinguished by a higher initial level of knowledge, under autarky and free trade, I find that under free trade the LDC (DC) experiences rates of technical progress and GOP growth less than or equal (greater than or equal) to those enjoyed under autarky. Unless the LDC's population is several orders of magnitude greater than that of the DC and the initial technical gap between the two economies is not large, the LDC will be unable to catch up with its trading partner. Hence, in terms of technical progress and growth, the LDC experiences dynamic losses from trade, whilst the DC experiences dynamic gains. However, since technical progress abroad can improve welfare at home, LDC consumers may enjoy - higher intertemporal utility along the free trade path. In the case of DC consumers, as long as their economy is not overtaken by the LDC they will enjoy both more rapid technical progress and the traditional static gains from trade, and hence experience an unambiguous improvement in intertemporal welfare.

If workers self-select into industries based upon their relative productivity in different tasks, and comparative advantage is aligned with absolute advantage, then the average efficacy of a sector's workforce will be negatively correlated with its employment share. This might explain the difference in the reported productivity growth of contracting goods and expanding services. Instrumenting with defense expenditures, I find the elasticity of worker efficacy with respect to employment shares is substantially negative, albeit estimated imprecisely. The estimates suggest that the view that goods and services have similar productivity growth rates is a plausible alternative characterization of growth in developed economies.

Measures of real consumption based on the ownership of durable goods, the quality of housing, the health and mortality of children, the education of youths, and the allocation of female time in the household indicate that sub-Saharan living standards have, for the past two decades, been growing about 3.4–3.7 percent per year, that is, three and a half to four times the rate indicated in international data sets.

With minimal sleight of hand, it is possible to transform the recent growth experience of the People's Republic of China from the extraordinary into the mundane. Systematic understatement of inflation by enterprises accounts for 2.5 percent growth per year in the nonagricultural economy during the first two decades of the reform period (197898). The usual suspects (i.e., rising participation rates, improvements in educational attainment, and the transfer of labor out of agriculture) account for most of the remainder. The productivity performance of the nonagricultural economy during the reform period is respectable but not outstanding. To the degree that the reforms have improved efficiency, these gains may lie principally in agriculture.

An increase in the size (scale) of an economy increases the total quantity of rents that can be captured by successful innovators, which, in equilibrium, should lead to a rise in innovative activity. Conventional wisdom and the theoretical predictions of models of endogenous innovation suggest that this increased research effort should lead to more rapid growth. As noted by Charles Jones, this prediction is at odds with the postwar experience of the OECD, where the growth of the market has indeed led to an increased R & D effort that, however, has been translated into stagnat or declining growth rates. Drawing on the remarkable insights of the museum curator Seabury C. Gilfillan, this paper modifies models of endogenous innovation to allow for the possibility that a rise in the profitability of innovative activity could lead to an increased variety of differentiated solutions to similar problems. An increased variety of technologies (e.g., an increase in the number and types of contraceptives) will increase the level of utility of the average consumer. If, however, continued improvement of this increased variety of technologies requires increased research input, a rise in the scale of the market could raise the equilibrium quantity of R & D without increasing the economy's growth rate.

This paper attempts to integrate traditional models of invention and learning by doing, developing a model that emphasizes the interdependence between research activity in the laboratory and production experience on the factory floor. Learning depends on invention in that learning by doing is viewed as the exploration of the finite and bounded productive potential of invented technologies. At the same time, the profitability of costly invention is dependent on learning in that costs of production depend on cumulative learning experience.

This paper attempts to integrate traditional models of invention and learning by doing, developing a model that emphasizes the interdependence between research activity in the laboratory and production experience on the factory floor. Learning depends on invention in that learning by doing is viewed as the exploration of the finite and bounded productive potential of invented technologies. At the same time, the profitability of costly invention is dependent on learning in that costs of production depend on cumulative learning experience. The model is a true hybrid, allowing for circumstances in which either the incentives to engage in research and/or the incentives to produce different goods are the binding constraints on growth.