Omitted-Ability Bias and the Increase in the Return to Schooling

Over the 1980s there were sharp increases in the return to schooling estimated with conventional wage regressions. We use both a signaling model and a human capital model to explore how the relationship between ability and schooling could have changed over this period in ways Chat would have increased the schooling coefficient in these regressions. Our empirical results reject the hypothesis that an increase in the upward bias of the schooling coefficient, due to a change in the relationship between ability and schooling, underlies the observed increase in the return to education over the 1980s. We also find that the increase in the return to education has occurred largely for workers with relatively high levels of academic ability.

Mathematical Models and Biological Meaning: Taking Trees Seriously

We compare three basic kinds of discrete mathematical models used to portray phylogenetic relationships among species and higher taxa: phylogenetic trees, Hennig trees and Nelson cladograms. All three models are trees, as that term is commonly used in mathematics; the difference between them lies in the biological interpretation of their vertices and edges. Phylogenetic trees and Hennig trees carry exactly the same information, and translation between these two kinds of trees can be accomplished by a simple algorithm. On the other hand, evolutionary concepts such as monophyly are represented as different mathematical substructures are represented differently in the two models. For each phylogenetic or Hennig tree, there is a Nelson cladogram carrying the same information, but the requirement that all taxa be represented by leaves necessarily makes the representation less efficient. Moreover, we claim that it is necessary to give some interpretation to the edges and internal vertices of a Nelson cladogram in order to make it useful as a biological model. One possibility is to interpret internal vertices as sets of characters and the edges as statements of inclusion; however, this interpretation carries little more than incomplete phenetic information. We assert that from the standpoint of phylogenetics, one is forced to regard each internal vertex of a Nelson cladogram as an actual (albeit unsampled) species simply to justify the use of synapomorphies rather than symplesiomorphies.Comment: 15 pages including 6 figures [5 pdf, 1 jpg]. Converted from original MS Word manuscript to PDFLaTe

Fertility Timing, Wages, and Human Capital

Women who have first births relatively late in life earn higher wages. This paper offers an explanation of this fact based on a staple life-cycle model of human capital investment and timing of first birth. The model yields conditions (that are plausibly satisfied) under which late childbearers will tend to invest more heavily in human capital than early childbearers. The empirical analysis finds results consistent with the higher wages of late childbearers arising primarily through greater measurable human capital investment.

The Effects of Technological Change on Earnings and Income Inequality inthe United States

This paper explores the relationship between technological change and inequality in the U.S. since the late 1960's. The analysis focuses primarily on studying patterns and trends in the dispersion of various distributions of earnings and income during this recent period of rapid technological progress. We review relevant literature and perform several empirical analyses using microdata from the March Current Population Surveys from 1968 to 1986. Our main findings are that there is little empirical evidence that earnings inequality, measured across individual workers, has increased since the late 1960's, and even less evidence to support the hypothesis that any changes that have occurred have resulted from the effect of technological change on the demand for labor. However, we do find evidence of an increase since the late 1960's in the inequality of total family income, measured across families. Moreover, much of the increase appears to be due to changes in family composition and labor supply behavior, suggesting that the main effects of recent technological change on inequality have been supply-side in nature.

Changes in the Structure of Family Income Inequality in the United States and Other Industrial Nationa During the 1980s

We examine the detailed structure of family income inequality in the United States, Canada, and Australia at various points during the 1980s. In each of these countries we find that income inequality increased among married couple families and that the increases are closely associated with increases in the inequality of husbands' earnings. However, only in the United States is the increased inequality of husbands' earnings also associated with an increase in education-earnings differentials. In addition, increased earnings inequality is associated with increases in both the variance of wages and the variance of labor supply in the United States and Canada, but only with an increase in the variance of labor supply in Australia. Evidence of an increase in married-couple income inequality is found for France and the United Kingdom, but not for Sweden or the Netherlands. For married couple families in Canada, Sweden, the United Kingdom, and the United States, we find that increased inequality of family income is closely associated with an increased correlation between husbands' and wives' earnings. A more detailed examination of this correlation in Canada and the United States suggests that the increase in this correlation cannot be explained by an increase in the similarity of husbands' and wives' observable labor market characteristics in either country. Rather, it is explained partly by changes in the way those characteristics translate into labor market outcomes and, more important, by changes in the interspousal correlation between unobservable factors that influence labor market outcomes.

The Distribution of Family Income: Measuring and Explaining Changes in the 1980s for Canada and the United States

This paper attempts to measure and explain recent changes in the distributions of family income in Canada and the U.S. using comparable micro-data for the two countries for 1979 and 1987. Three main sets of conclusions are reached. First, the distributions of total family income (pre-tax, post-transfer) in the two countries changed differently in the 1980s. Average family income increased faster in Canada than in the U.S.. though income inequality increased unambiguously in the U.S., but not in Canada. Imposing a simple structure on the data reveals that the social welfare implications of these changes are generally indeterminate for each country. Second, changes in the distribution of transfer income had important influences on the distribution of total family income in both Canada and the U.S. Transfer income in Canada increased more rapidly than it did in the U.S. during the 1980s and also became more redistributive in nature. Most notably, the shifts in transfer income left female-headed families in Canada with a higher mean income and less income inequality in 1987 than they had in 1970. Among female-headed families in the U.S., income inequality increased while average income declined. Third, increased income inequality in the U.S. partly reflects increased earnings inequality, which is itself associated with a widening of education-earnings differentials that occurred in the 1980s. Earnings inequality also increased in Canada in the 1980s, despite the stability of education-earnings differentials.

The Storm-Track Response to Idealized SST Perturbations in an Aquaplanet GCM

The tropospheric response to midlatitude SST anomalies has been investigated through a series of aquaplanet simulations using a high-resolution version of the Hadley Centre atmosphere model (HadAM3) under perpetual equinox conditions. Model integrations show that increases in the midlatitude SST gradient generally lead to stronger storm tracks that are shifted slightly poleward, consistent with changes in the lower-tropospheric baroclinicity. The large-scale atmospheric response is, however, highly sensitive to the position of the SST gradient anomaly relative to that of the subtropical jet in the unperturbed atmosphere. In particular, when SST gradients are increased very close to the subtropical jet, then the Hadley cell and subtropical jet is strengthened while the storm track and eddy-driven jet are shifted equatorward. Conversely, if the subtropical SST gradients are reduced and the midlatitude gradients increased, then the storm track shows a strong poleward shift and a well-separated eddy-driven jet is produced. The sign of the SST anomaly is shown to play a secondary role in determining the overall tropospheric response. These findings are used to provide a new and consistent interpretation of some previous GCM studies concerning the atmospheric response to midlatitude SST anomalies

Private languages and private theorists

Simon Blackburn objects that Wittgenstein's private language argument overlooks the possibility that a private linguist can equip himself with a criterion of correctness by confirming generalizations about the patterns in which his private sensations occur. Crispin Wright responds that appropriate generalizations would be too few to be interesting. But I show that Wright's calculations are upset by his failure to appreciate both the richness of the data and the range of theories that would be available to the private linguist