witnessed a fall in the wage premium. Given that the relative supply of this group continued growing at a substantial rate, the relative demand must not have changed significantly. The evidence for Colombia in Table 3.2 indicates the presence of stronger relative demand forces for high school workers in the 1990s than in the 2000s. The wage premium fell very little in the context of a large increase in the relative supply of workers with secondary education in 1996-2000, while with an expansion rate of about half that in the previous period the wage premium fell substantially more, indicating a shift in the relative demand towards this group with respect to workers without a high school degree.

The results for Costa Rica in Table 3.1 indicate that the relative supply of skilled workers in Costa Rica increased at an annual rate of 4 percent in the 1990s, and of 3.4 percent in the 2000s. Although Figure C1 in the appendix below indicates substantial fluctuations over the period, the wage gap increased slightly in the 1990s, in particular at the end of the decade. The wage premium fell between 2002 and 2005 but started to increase again in the second half of the decade. Nevertheless, the overall change 2002-2009 is negative, although small. Given the increase in the relative supply, this small change is consistent, given the assumed elasticities of substitution, with a small positive shift in relative demand, smaller than in the 1990s. Table 3.2, in turn, indicates that the relative supply of semi-skilled workers (with respect to high school dropouts) increased in both periods at an accelerating rate, with relatively minor changes in the high school skill premium – negative in the 1990s and positive in the 2000s. A notable difference in the case of Costa Rica is that the relative increase of the high skill group was larger than that of the middle skill group. The evidence indicates the presence of stronger relative demand forces for high school graduate workers in 2002-2009 than in the 1990-2002 period: demand factors must have operated in the most recent years, since the relative wage of high skill workers increased moderately with simultaneous increase in its relative supply.

Data limitations in the case of Ecuador restrict the comparability of the available surveys from the 1990s with those of the 2000s. The analysis here is based on comparable statistics constructed for the 2000s, based on the ENEMDU survey. The wage skill premium fell at an annual rate of 3.2 percent between 2003 and 2010, while the relative supply increased steadily in the same period. This indicates that, conditional on the assumptions on elasticities of substitution, the relative demand for skilled labor must have fallen over that period. With respect to unskilled workers, the increase in the relative supply of the high school group resulted in a reduction of its wage premium over the 20032010 period. This pattern is similar to that of the aggregate skilled-unskilled premium and relative demand, although the changes are smaller for the high school-dropout differentials. As in the cases of Colombia and Costa Rica, Tables 3.1 and 3.2 indicate that most of the reduction in the share of employment of the low skill group was accounted for by an increase of that of the high skill group, although, as discussed in the sector decompositions section, in the case of Ecuador there were relatively large within and between sector effects for both skill groups.

Table 3.1 indicates that the relative supply of skilled labor increased strongly in El Salvador during the 1990s. The corresponding wage premium also increased significantly during that decade, and these simultaneous trends are consistent with a strong increase in the relative demand for skilled labor. The evolution of these variables in the decade of 2000, however, indicates a marked change. The relative labor supply of skilled labor stopped growing, while the corresponding wage premium 42