The trends observed in Table 2 (the disproportionate decline in the work hours of low wage workers between the 1890s and 1973 and the increase in the work hours of high paid workers and the decrease in hours of low paid workers between 1973 and 1991) persist even within groups of male workers.11 Within wage deciles the lower paid workers worked the longest day in the 1890s whereas the higher paid workers worked the shortest day in 1991. Furthermore, the relationship between daily hours and the wage rate observed in Table 2 is seen within all occupation and industry categories (see Tables 4 and 5), implying that the pattern is not solely due to changes on the factory floor. The pattern persists within age groups and within occupation and industry groups controlling for age, marital status, number of dependents, and state and year fixed effects as well. Between 1973 and 1991 the dispersion in hours by wage decile among men working less than 40 hours a week (and hence not subject to legal overtime provisions) widened, suggesting that disproportionate increases in overtime rates of pay cannot explain the changing hours pattern.

Although micro data do not exist to ascertain exactly when between the 1890s and 1973 the distribution of the length of the work day became more compressed, the trend in the mean length of the work day suggests that most of the compression occurred by 1920. The length of the work day for manufacturing workers was 10.0 hours in 1895 and 9.3 in 1914 (Series D 845-876 in U.S Bureau of the Census 1975: 172) and by 1919 eight hour work days were the norm (U.S. Department of Labor 1920: 37). Recall that Table 2 showed that the decline in hours worked between the 1890s and 1973 was largest among men earning the lowest wages. Therefore most changes in the mean length of the work day probably came from disproportionate changes in the hours of men in the lowest deciles of the wage distribution.