I am Assistant Professor of Social Science at HKUST. My work primarily contributes to three areas of research: (1) patterns of health and mortality, (2) impacts of large-scale shocks such as wars and economic crises, and (3) internal and international migration. These research areas are unified by my broader interest in how the social stratification system intersects with population dynamics across historical and contemporary contexts.
Research Interests
Population studies; mortality and longevity; aging and the life course; global health; social stratification; income inequality; migration and immigration; armed conflicts; pension systems; demographic and quantitative methods; historical demography; family
Publications
Shi, Jiaxin, and Jason Fletcher. Forthcoming. Citizenship and immigrant longevity: Evidence from U.S. census-linked Social Security Administration death records. Demography.
There has been considerable interest among social science researchers in understanding the health and longevity disparities between immigrants and nonimmigrants. An emerging literature has highlighted that the health of immigrants varies by immigrant characteristics such as socioeconomic status and country of origin. Despite these insights, one aspect that remains underexplored is how citizenship status may influence immigrants’ health. To address this gap, we examine the effects of citizenship status on the longevity of immigrants and their children for immigrants who lived in the early-20th-century America. Using a novel dataset that links Social Security Administration death records (1975–2005) to full-count U.S. census (1920–1940), we find that naturalization increased longevity for first- and second-generation immigrant men. Citizenship increased foreign-born men’s longevity by 7.5 months, and fathers’ citizenship increased sons’ longevity by 4.1 months. For sons, their fathers’ socioeconomic status and own socioeconomic achievement in early adulthood partly explained the effects of father’s citizenship status. Moreover, obtaining citizenship earlier in life appears to be linked to longer lifespans, indicating the importance of the timing of citizenship's effects. We also find that the benefits of citizenship were first stable, then increased, and later decreased at more advanced ages.
Shi, Jiaxin, and Jason Fletcher. 2025. Trend breaks in US life expectancy over 120 years and potential sources of future gains. Population Studies.
Research indicates a significant slowdown in US life expectancy growth post-2010, marking a departure from the consistent longevity progress throughout the twentieth century. We extend this understanding, tracing the deceleration of US life expectancy back to the 1950s, after which the average decadal change dropped from 3.80 to 1.61 years. Surprisingly, these mid-twentieth-century shifts were consistent across race and sex in the United States as well as in other high-income countries. Using a simple approach of quantifying potential life expectancy gains through eliminating age-specific mortality, we find that, the role of reducing midlife mortality in life expectancy has been more significant in the United States than in other countries since 1900. The findings suggest that US life expectancy is unlikely to progress at the high speed observed between 1900 and 1950s, with future advancements hinging on the reduction of old-age mortality, particularly from cardiovascular and mental and nervous system diseases.
At older ages, most people are supported by pension systems that provide payments based on prior contributions. An important, but neglected, aspect of inequality in how much people receive in pensions is the number of years they live to receive their pension. We examine inequality in lifetime-accumulated pensions and show the importance of mortality for understanding inequalities in pension payments, and contrast it to inequalities in working-age earnings and yearly pension payments among older adults. In contrast to most previous research on old-age inequality comparing different social groups, we focused on total-population-level inequality. Using Swedish register data covering the retired population born from 1918–1939, we found that lifetime pensions are much more unequal than pre-retirement earnings and yearly pensions. Our findings also show that mortality explains more than 50 percent of the inequality of lifetime pensions within cohorts, and plays an important role in explaining changes in inequality across cohorts (192 percent among men and 44 percent among women). Pension policies can affect lifetime pension inequality, but such effects are limited in magnitude unless they directly affect the number of years of receiving pensions.
Shi, Jiaxin, Christian Dudel, Christiaan Monden, and Alyson van Raalte. 2023. Inequalities in retirement lifespan in the United States. Journal of Gerontology, Series B: Social Sciences.
The length of retirement life may be highly unequal due to persistent and significant discrepancies in old-age mortality. This study assesses gender and educational differences in the average retirement life span and the variation in retirement life span, taking into account individual labor force exit and reentry dynamics. We used longitudinal data from the Health and Retirement Study from 1996 to 2016, focusing on respondents aged 50 and older (N = 32,228). Multistate life tables were estimated using discrete-time event history models. The average retirement life span, as well as absolute and relative variation in retirement life span, were calculated analytically. Among women, we found a persistent educational gradient in average retirement life span over the whole period studied; among men, the relationship between education and retirement expectancy differed across periods. Women and the lower-educated had higher absolute variation in retirement life span than men and the higher-educated—yet these relationships were reversed when examined by relative variation. Our multistate approach provides an accurate and comprehensive picture of the retirement life span of older Americans over the past two decades. Such findings should be considered in high-level discussions on Social Security. Potential reforms such as raising the eligibility age or cutting benefits may have unexpected implications for different social groups due to their differential effects on retirement initiation and reentry dynamics.
Shi, Jiaxin, José Manuel Aburto, Pekka Martikainen, Lasse Tarkiainen, and Alyson van Raalte. 2023. A distributional approach to measuring lifespan stratification. Population Studies.
The study of the mortality differences between groups has traditionally focused on metrics that describe average levels of mortality, for example life expectancy and standardized mortality rates. Additional insights can be gained by using statistical distance metrics to examine differences in lifespan distributions between groups. Here, we use a distance metric, the non-overlap index, to capture the sociological concept of stratification, which emphasizes the emergence of unique, hierarchically layered social strata. We show an application using Finnish registration data that cover the entire population over the period from 1996 to 2017. The results indicate that lifespan stratification and life-expectancy differences between income groups both increased substantially from 1996 to 2008; subsequently, life-expectancy differences declined, whereas stratification stagnated for men and increased for women. We conclude that the non-overlap index uncovers a unique domain of inequalities in mortality and helps to capture important between-group differences that conventional approaches miss.
Shi, Jiaxin, and Martin Kolk. 2022. How does mortality contribute to lifetime pension inequality? Evidence from five decades of Swedish taxation data. Demography.
As with many social transfer schemes, pension systems around the world are often progressive: individuals with lower incomes receive a higher percentage of their income as a subsequent pension. On the other hand, those with lower earnings have higher mortality and thus accumulate fewer years of pension income. Both of these opposing factors influence the progressiveness of pension systems. Empirical efforts to disentangle the effects of mortality inequality on lifetime pension inequality have been scarce. Using Swedish taxation data linked with death registers for 1970–2018, we study how education and preretirement earnings relate to lifetime pensions from age 60 onward and how mortality inequalities contribute to overall inequalities in lifetime pensions. The results show that a progressive replacement structure and mortality differences contribute to the overall distribution of pension payments over the life course. Up to one quarter of lifetime pension inequality is attributable to the greater longevity of socially advantaged groups—particularly among men. Hence, mortality inequalities are an important determinant of the overall degree of between-group income transfers in a pension system, but they are not as important as inequalities in prior earnings.
Permanyer, Iñaki, and Jiaxin Shi. 2022. Normalized lifespan inequality: Disentangling the longevity-lifespan variability nexus. Genus.
Previous studies have documented a historically strong and negative association between countries’ life expectancy (i.e., average longevity) and length-of-life inequality (i.e., variability in ages at death). The relationship between both variables might be partially explained by life expectancy increasing at a faster pace than maximal length of life, a phenomenon that mechanically compresses the age-at-death distribution and has not been taken into consideration in previous studies. In this paper, we propose a new approach to lifespan inequality measurement that accounts for the (uncertainly) bounded nature of length-of-life. Applying the new approach to the countries of the Human Mortality Database, we observe that the decline in overall lifespan variability typically associated with increases in longevity seems to stop and even reverse at higher levels of life expectancy. This suggests the emergence of worrying ethical dilemmas, whereby higher achievements in longevity would only be possible at the expense of higher lifespan variability.
Shi, Jiaxin, Lasse Tarkiainen, Pekka Martikainen, and Alyson van Raalte. 2021. The imapct of income definitions on mortality inequalities. SSM-Population Health.
Income is a strong predictor of adult mortality. Measuring income is not as simple as it may sound. It can be conceptualized at the individual or the household level, with the former better reflecting an individual's earning ability, and the latter better capturing living standards. Furthermore, respondents are often grouped into income categories based on their positions in the income distribution, and this operationalization can be done on the basis of age-specific or total population income distributions. In this study, we look at how four combinations of different conceptualizations (individual vs. household) and operationalizations (age-specific vs. total population) of income can affect mortality inequality estimates. Using Finnish registry data, we constructed period life tables for ages 25+ from 1996 to 2017 by gender and for four income definitions. The results indicated that the slope index of inequality for life expectancy varied by 1.1–5.7 years between income definitions, with larger differences observed for women than for men. The overall age patterns of relative index of inequality for mortality rates yielded by the four definitions were similar, but the levels differed. The period trends across income definitions were consistent for men, but not for women. We conclude that researchers should pay particular attention to the choice of the income definitions when analyzing the association between income and mortality, and when comparing the magnitude of inequality across studies and over time.
Riffe, Tim, Enrique Acosta, and the COVerAGE-DB team. 2021. Data Resource Profile: COVerAGE-DB: a global demographic database of COVID-19 cases and death. International Journal of Epidemiology.
Selected Ongoing Projects
Shi, Jiaxin, and Jason Fletcher. Geographic mobility and mortality. (R&R at Demography)
Shi, Jiaxin, and Jason Fletcher. The Hidden Toll of WWII over Seven Decades: An Analysis of 12 High-Income Countries. (R&R at Demography)
Hagley, Marcus Immonen, Jiaxin Shi, and Linda Kridahl. Family deaths and retirement timing. (Under review)
Shen, Tianyu, and Jiaxin Shi. Inequalities in health-adjusted retirement life expectancy (Under review)
Shi, Jiaxin, and Martin Kolk. Income inequalities over the life course. (draft available)
Pan, Guanghui, and Jiaxin Shi. Heterogeneous widowhood effects. (draft available)
John, Ben Malinga, Emanuel Souza, and Jiaxin Shi. 74 years of Malawi's life expectancy gains: An international comparison. (draft available)
Shi, Jiaxin, Jason Fletcher. Discrimination and immigrant longevity: Evidence from anti-German sentiment during WWI.
Shi, Jiaxin, and Martin Kolk. Backward and forward perspectives on migrant retention.
Shi, Jiaxin, Pavel Grigoriev, and Sebastian Klüsener. Metropolitan Longevity: Advantage or Disadvantage?
Zhao, Xinyi, and Jiaxin Shi. Estimating internal migration of scholars around the globe using bibliometric data.
Teaching
SOSC 1110 Data Analysis for Quantitative Social Research (spring 2026)
SOSC 3400 Population Health (spring 2026)
Selected Awards
Otto Hahn Medal from the Max Planck Society, 2024
Alan C. Kerckhoff Award, RC28, 2022
Graduate Student Travel Award, RC28, 2017
Poster Award, Wittgenstein Centre Conference, 2019
Asian Future Leader Scholarship, Bai Xian Asia Institute, 2016