1 Dynamic Changes of Social Mobility in Japan 1955-95

Many past researches on social mobility exhibits that mobility chance (unequal opportunity in intergenerational mobility) in industrialized societies is stable over time. However, those studies do not thoroughly capture dynamic changes in mobility chance because they do not identify and examine the three types of effects; period effect, cohort effect, and age effect. Focusing on ‘overall ’ and ‘class-specific ’ mobility chances, this paper explores the dynamic changes of intergenerational mobility in Japan by using the SSM national survey data collected every 10 years from 1955 to 1995. The results of analysis to mobility tables which are made by the classification of six social classes exhibit that overall mobility chance measured by ‘achieved ratio of perfect mobility ’ was equalized by the period effect in the period of 1955-65, and since 1965 it has been affected by the cohort effect that brought constancy for the cohort born in 1900-29, equalization for the cohort in 1930-49 cohort, and increase of inequality for the cohort in 1960-69. When class-specific mobility chance (degree of class inheritance) is measured by log of odds ratio, all types of effects are found. However, the age effect is found in only one of six classes and stable over time. Therefore, the major determinants to form the changes in overall mobility chance were the cohort and the period effects. Most of the cohort effects found in four classes have intensified inequality, but progressed very gradually. The period effects in four classes happened temporally at different periods, but most of the effects had strong influence in bringing equality. Eventually, the class-specific period effects equalized the overall mobility chance in Japan until the 1950-59 cohort. The analysis identifying the three types of effects shows the complicated dynamics of changes that the past studies have overlooked. The gradual cohort effects and the intermittent period effects that were inherent to individual classes contributed to the changes of overall mobility chance over time