4. In comparison with the rates of unemployment of the 1950s and 1960s, the unemployment rate of the 1970s is biased upward for two reasons. First, as a result of the work registration requirement passed in the early 1970s, some persons are now counted as unemployed who previously were not. Second, there have been significant changes in the age-sex composition of the work force. Youthful and women workers, who generally experience higher rates of unemployment, comprised an increasing share of the labor force during the 1970s. Thus, it is not surprising that the rate of unemployment during the 1970s was significantly higher than the rates during the two previous decades even though the rates of employment for all three decades were similar.