ECONOMIC

tion about lifetime work experience. The National Longitudinal Survey(NLS), a large data source sponsored by the Department of Labor, hasrecently become available and provides much more detailed informationon the work histories of women than has ever been previously compiled.The survey indicates that in 1967, among married women 30 to 44 yearsold with children, only 3 percent had worked at least 6 months every yearsince leaving school. On the average, married women worked at least 6months in 40 percent of their years after leaving school, but the workwas not likely to be continuous.One study which used the NLS showed that earnings of women do risewith experience and that continuity of experience, as opposed to intermittentparticipation, commands a premium. Withdrawal from the labor forcefor a time resulted in a decline in earnings when work resumed, since previouslyaccumulated skills, or human capital, actually depreciate duringextended periods away from work. For the married women in the sample,the hourly wage rate was about 66 percent of that of married men in thesame age group (30-44 years) in the same year (1966), after controlling fordifferences in years of schooling. At least half of the 34 percent differentialresulted from differences in their measured experience. The remaining differentialis unexplained.It is not known to what extent current discrimination, as opposed toother unmeasured factors, contributed to this differential. For example,the study could not provide direct measures of the nature of the investmentsmade in the productivity of women and men, other than years offormal schooling. Women do not appear to obtain as much training on thejob as men for the same length of time in the labor force. Thus, althoughwomen's earnings rise with experience, the study found that they do not riseas steeply as men's. This difference could result partly from a faulty measurementof a year's experience for women; as noted above, in these data a year'swork could be as little as 6 months of part-time employment. However, themeasured effect of experience could also be interpreted as the result of discrimination.That is, employers may deny a woman on-the-job training or apromotion because of her sex, sometimes from sheer prejudice, sometimesbecause they think a woman is more likely to quit for personal reasons. Onecan also surmise that women themselves may not choose to invest in trainingat a cost of either lower current earnings or additional hours of work, whenthe payoff might be lost because of the uncertainty of their future workpatterns.For example, women in school have a lower enrollment rate in programsoriented toward the labor market—engineering, accounting, electronics—and a higher enrollment rate in courses that may be more applicable to workor leisure in the home—child development, languages, literature. This patternmay reflect greater uncertainty among women about their future attachmentto the labor force. A choice of field of study may also be influenced155