changes across and within occupations indicates that most of these changes in recent years have occurred within occupations. This does not necessarily imply that occupational classifications were increasingly challenged. But it does imply that there was increasing diversity of the workforce and requirements of workers within narrow occupational groupings. If this diversity is also associated with diversity in the content of work and the skills of workers, which seems particularly likely given the findings for tenure and training, then it is more likely that occupational classifications may have to be reevaluated.
The other salient change in recent decades is the sharp increase in the dispersion of wages or wage inequality. Most economic research on this topic focuses on either within-group or between-group inequality, with groups typically defined by education, age, and experience. Thus, for example, between-group inequality may refer to the wage (or earnings) differential between workers with a high school diploma and workers with a college degree, whereas within-group inequality may refer to the dispersion of wages for those with a college degree. Recent research has clearly established that, for education, age, and experience groups, both between-group and within-group wage inequality has increased substantially over the past two decades (see, for example, Blackburn et al., 1990; Bound and Johnson, 1992; and Katz and Murphy, 1992). For example, wage differentials between college and high school graduates have widened, as has the dispersion of wages for high school students.
The rise in both components of inequality, especially the between-group component, has been linked to increased relative demand for workers with higher educational attainment, stemming in part, perhaps, from the diffusion of computers in the workplace, but due no doubt to other factors as well, such as intensified competition in global and domestic product markets, the decline of unions, and declines in the ratio of the minimum wage to average wages in the economy. To some extent, then, rising