This study examines the limitations of income mobility indicators, which are mainly used in existing studies, and presents the results of applying the analysis method of Krebs et al.(2019) to Korean survey data. The temporary income shock on residual income, which is not explained by individual characteristics such as education, job career, age, and so on, increases income mobility, but has a small impact on social welfare. On the other hand, the faster the permanent income shock disappears, the faster the difference between the residual income of low- and high-income earners decreases, and the higher the income mobility and social welfare. Of course, the greater the variance of the initial permanent income variance, and the greater the magnitude of the permanent income impact afterwards, the higher the income mobility but the lower the social welfare. In addition, 80 percent of one-year short-term income mobility was analyzed due to temporary shocks, including measurement errors, so it seems desirable to analyze income mobility analysis at least over the span of three years.

Korea’s income mobility itself is analyzed to have increased further since around 2012, but social welfare has decreased. This implies that the analysis of income mobility indicators themselves should not be the sole purpose of analysis. In order to increase social welfare as well as increase income mobility, it seems necessary to reduce the persistence of permanent shocks and reduce the size of external economic shocks that result in changes in residual income.

Even if income mobility is slightly reduced after tax, personal income tax acting as a buffer that can alleviate the size of income shocks increases social welfare. In this regard, it seems necessary to impose more burden on high-income earners of health insurance premiums and national pension premiums. the government cash transfer, which is being provided for the purpose of protecting the vulnerable, rather significantly reduced income mobility and social welfare, which seems due to the sharp increase in the portion of government cash transfer given to the top 40 percent earners comparing to 2007-2008. It is necessary, through further review, to be more careful in setting the beneficiaries of policy measures so that government cash transfer can be concentrated on the vulnerable.

The new income mobility analysis method introduced in this study can be applied to the study for income tax reform through a more detailed analysis for each component of income tax. However, this will be possible only when the National Tax Service has wider access to detailed items on individual income tax return form. In addition, the portion of government cash transfer given to high-income earners is also deemed for further review using administrative data.

Preface
Executive Summary

Chapter 1 Introduction

Chapter 2 Review of Existing Literature
　Section 1 Necessity of the Study
　Section 2 Existing Domestic Studies
　Section 3 Existing International Studies

Chapter 3 Trends in Traditional Income Mobility Indicators
　Section 1 Relative Income Mobility
　Section 2 Absolute Income Mobility
　Section 3 Variance Analysis

Chapter 4 Krebs' New Method of Income Mobility Analysis
　Section 1 Income Mobility Linked to Social Welfare
　Section 2 Results of Income Mobility Measurement by Krebs and Social Welfare Analysis
　Section 3 Key Tax and Fiscal Policies, Income Mobility, and Social Welfare

Chapter 5 Conclusion

References
Appendix
ABSTRACT