Life Cycle Bias in the Estimation of Intergenerational Earnings Persistence

The estimation of intergenerational earnings mobility is rife with measurement problems since the research does not observe permanent, lifetime earnings. Nearly all studies make corrections for mean variation in earnings because of the age differences among respondents. Recent works employ average earnings or instrumental variable methods to address the effects of measurement error as a result of transitory earnings shocks and mis-reporting. However, empirical studies of intergenerational mobility have paid no attention to the changes in earnings variance across the life cycle suggested by economic models of human capital investment. Using information from the Intergenerational Income Data from Canada and the National Longitudinal Survey and Panel Study of Income Dynamics from the United States, this study finds a strong association between age at observation and estimated earnings persistence. Part of this age-dependence is related to a general increase in transitory earnings variance during the collection of data. An independent effect of life cycle investment is also identified. These findings are then applied to the variation among intergenerational earnings persistence studies. Among studies with similar methodologies, one-third of the variance in published estimates of earnings persistence is attributable to cross-study differences in the age of responding fathers. Finally, these results call into question tests for the importance of credit constraints based on measures of earnings at different points in the life cycle.