The US gender pay gap in the 1990s2004

"We use data from the Michigan Panel Study of Income Dynamics (PSID) to study the slowdown in the convergence of female and male wages in the 1990s compared to the 1980s. We found that changes in human capital did not contribute to the trends, since women improved their relative human capital to a comparable extent in the 1980s and the 1990s. Occupational upgrading of women and deunionization explained a portion of the slower 1990s convergence since the positive effect of these factors on women's relative wage gains was larger in the 1980s. However, the largest factor accounting for the slowing of wage convergence was the trend in the "unexplained gap," which was sufficient to more than fully account for the slowdown in wage convergence in the 1990s. Factors that may have contributed to the slower narrowing of the unexplained gender pay gap include changes in labor force selectivity, changes in gender differences in unmeasured characteristics and labor market discrimination, and changes in the favorableness of supply and demand shifts. We find some evidence consistent with each of these factors suggesting that each may have played a role in explaining the observed trends"--National Bureau of Economic Research web site.